kundu (exact): 645 papers, Hirsch index 37, Hirsch ratio 0.057.
adsauthor "Kundu, M.R." abstract
@--------------------------------------------------------------------
Title: Microflares and the Statistics of X-ray Flares
Authors: Hannah, I. G.; Hudson, H. S.; Battaglia, M.;
Christe, S.; Kasparová, J.; Krucker, S.;
Kundu, M. R.; Veronig, A.
Bibliographic Code: 2011SSRv..159..263H, eprint = 1108.6203
Abstract
This review surveys the statistics of solar X-ray flares, emphasising
the new views that RHESSI has given us of the weaker events (the
microflares). The new data reveal that these microflares strongly
resemble more energetic events in most respects; they occur solely
within active regions and exhibit high-temperature/nonthermal emissions
in approximately the same proportion as major events. We discuss the
distributions of flare parameters (e.g., peak flux) and how these
parameters correlate, for instance via the Neupert effect. We also
highlight the systematic biases involved in intercomparing data
representing many decades of event magnitude. The intermittency of the
flare/microflare occurrence, both in space and in time, argues that
these discrete events do not explain general coronal heating, either in
active regions or in the quiet Sun.
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Title: The Relationship Between Solar Radio and Hard X-ray
Emission
Authors: White, S. M.; Benz, A. O.; Christe, S.; Fárník, F.;
Kundu, M. R.; Mann, G.; Ning, Z.; Raulin, J.-P.;
Silva-Válio, A. V. R.; Saint-Hilaire, P.; Vilmer, N.;
Warmuth, A.
Bibliographic Code: 2011SSRv..159..225W, eprint = 1109.6629
Abstract
This review discusses the complementary relationship between radio and
hard X-ray observations of the Sun using primarily results from the era
of the Reuven Ramaty High Energy Solar Spectroscopic Imager satellite. A
primary focus of joint radio and hard X-ray studies of solar flares uses
observations of nonthermal gyrosynchrotron emission at radio wavelengths
and bremsstrahlung hard X-rays to study the properties of electrons
accelerated in the main flare site, since it is well established that
these two emissions show very similar temporal behavior. A quantitative
prescription is given for comparing the electron energy distributions
derived separately from the two wavelength ranges: this is an important
application with the potential for measuring the magnetic field strength
in the flaring region, and reveals significant differences between the
electrons in different energy ranges. Examples of the use of
simultaneous data from the two wavelength ranges to derive physical
conditions are then discussed, including the case of microflares, and
the comparison of images at radio and hard X-ray wavelengths is
presented. There have been puzzling results obtained from observations
of solar flares at millimeter and submillimeter wavelengths, and the
comparison of these results with corresponding hard X-ray data is
presented. Finally, the review discusses the association of hard X-ray
releases with radio emission at decimeter and meter wavelengths, which
is dominated by plasma emission (at lower frequencies) and electron
cyclotron maser emission (at higher frequencies), both coherent emission
mechanisms that require small numbers of energetic electrons. These
comparisons show broad general associations but detailed correspondence
remains more elusive.
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Title: High-Energy Emission from a Solar Flare in Hard
X-rays and Microwaves
Authors: Kundu, M. R.; Grechnev, V. V.; White, S. M.;
Schmahl, E. J.; Meshalkina, N. S.; Kashapova, L. K.
Bibliographic Code: 2009SoPh..260..135K, eprint = 0908.0385
Abstract
We investigate accelerated electron energy spectra for different sources
in a large flare using simultaneous observations obtained with two
instruments, the Nobeyama Radio Heliograph (NoRH) at 17 and 34 GHz, and
the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) at
hard X-rays. This flare is one of the few in which emission up to
energies exceeding 200 keV can be imaged in hard X-rays. Furthermore, we
can investigate the spectra of individual sources up to this energy. We
discuss and compare the HXR and microwave spectra and morphology.
Although the event overall appears to correspond to the standard
scenario with magnetic reconnection under an eruptive filament, several
of its features do not seem to be consistent with popular flare models.
In particular we find that (1) microwave emissions might be optically
thick at high frequencies despite a low peak frequency in the total flux
radio spectrum, presumably due to the inhomogeneity of the emitting
source; (2) magnetic fields in high-frequency radio sources might be
stronger than sometimes assumed; (3) sources spread over a very large
volume can show matching evolution in their hard X-ray spectra that may
provide a challenge to acceleration models. Our results emphasize the
importance of studies of sunspot-associated flares and total flux
measurements of radio bursts in the millimeter range.
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Title: The Morphology of Decimetric Emission from Solar
Flares: GMRT Observations
Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.;
Subramanian, P.; Ananthakrishnan, S.; Janardhan, P.
Bibliographic Code: 2006SoPh..236..369K
Abstract
Observations of a solar flare at 617 MHz with the Giant Meter-wave Radio
Telescope (GMRT) are used to study the morphology of flare radio
emission at decimetric wavelengths. There has been very little imaging
in the 500 1000 MHz frequency range, but it is of great interest,
since it corresponds to densities at which energy is believed to be
released in solar flares. This event has a very distinctive morphology
at 617 MHz: the radio emission is clearly resolved by the 30" beam
into arc-shaped sources seeming to lie at the tops of long loops,
anchored at one end in the active region in which the flare occurs, with
the other end lying some 200 000 km away in a region of quiet solar
atmosphere. Microwave images show fairly conventional behaviour for the
flare in the active region: it consists of two compact sources overlying
regions of opposite magnetic polarity in the photosphere. The decimetric
emission is confined to the period leading up to the impulsive phase of
the flare, and does not extend over a wide frequency range. This fact
suggests a flare mechanism in which the magnetic field at considerable
height in the corona is destabilized a few minutes prior to the main
energy release lower in the corona. The radio morphology also suggests
that the radiating electrons are trapped near the tops of magnetic
loops, and therefore may have pitch angles near 90˚.
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Title: Radio and Hard X-Ray Imaging Observations of the
M5.7 Flare of 2002 March 14
Authors: Schmahl, E. J.; Kundu, M. R.; Garaimov, V. I.
Bibliographic Code: 2006ApJ...643.1271S
Abstract
We describe a flare of GOES class M5.7 that was observed simultaneously
by RHESSI (Ramaty High Energy Solar Spectroscopic Imager) and NoRH
(Nobeyama Radio Heliograph). The flare occurred in AR 9866 located near
the disk center. The hard X-ray (HXR), microwave, EIT, and TRACE 195
Å observations indicate that the flaring region consisted of a
complex of multiple loops. In the microwave domain the source
morphology, the timing, the polarization characteristics, and the
photospheric magnetic fields clearly indicate that it is of a class
characterized as a ``double loop'' configuration, meaning two systems of
magnetic flux, each consisting of many smaller loops. The observations
suggest the existence of a small loop system created by the emergence of
new flux, which interacts with an old flux system, and of a remote flare
site that is observed primarily in radio. The former is the main flare
site where we observe microwave, HXR, and EUV emissions. In HXR there
are two main identifiable loop systems. The first is an elongated one
filled with energetic electrons primarily emitting lower energy (12-25
keV) HXR with a colocated microwave source; this source has distinct
footpoints at higher X-ray energies. The second loop system is implied
by compact HXR sources in opposite magnetic polarities separated by a
distance greater than the length of the first loop system. Spectroscopic
analysis of the RHESSI data shows that the spectrum can be fitted with a
thick-target model with a thermal component and a broken power-law
component of the electron energy distribution. This model is used to
address the thermal/nonthermal and radio/HXR electron number problems.
@--------------------------------------------------------------------
Title: Flare-Associated Decimeter TypeIV Bursts at High
Frequencies
Authors: Kundu, M. R.; White, S. M.; Hori, K.; Schmahl, E. J.
Bibliographic Code: 2006AGUSMSH24A..06K
Abstract
Type IV radio bursts are broadband continuum events associated with
solar flares that typically occur after the impulsive phase, can last
for tens of minutes and are usually confined to low frequencies, below
200 MHz. However some flares show clear evidence for strong Type IV-like
emission that is confined to high frequencies, around 1 GHz. Type IV
events require nonthermal electrons and imply the presence of either
long-lived energetic electrons trapped in coronal loops, or else ongoing
acceleration lasting for tens of minutes following a flare. If, as is
widely believed, the emission mechanism of Type IV bursts is plasma
emission, then the high- frequency events require electrons at densities
of over 3 109 cm-3, far higher densities than are involved in the low
frequency Type IV bursts. We present a sample of such high frequency
Type IV bursts and analyze their properties and association with other
flare phenomena, and discuss their possible sources.
@--------------------------------------------------------------------
Title: Nobeyama radio heliograph observations of RHESSI
microflares
Authors: Kundu, M. R.; Schmahl, E. J.; Grigis, P. C.;
Garaimov, V. I.; Shibasaki, K.
Bibliographic Code: 2006A&A...451..691K
Abstract
Aims.We present a summary of the analysis of thirty microflares,
observed simultaneously by the Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) in hard X-rays and by Nobeyama RadioHeliograph (NoRH) in
microwaves (17 GHz).
Methods: .We used microflares observed by
RHESSI in the energy range 3-25 keV, and for larger events, up to 35
keV. The observations were made 2002, May 2-6.
Results: .We
describe the imaging characteristics of these microflares including
their locations in hard X-rays and microwaves and the relative positions
of the micro-flaring sources. We discuss the brightness temperatures,
emission measures and their hard X-ray spectral properties. We see small
(mini) flaring loops clearly in NoRH and RHESSI images. The microwave
emission often seems to come from the RHESSI foot points (for higher
energies), and from the entire small (mini) flaring loop (for lower
energies). Sometimes the two (microwave and hard X-ray) sources
coincide, at other times they are at opposite ends of a mini flaring
loop. Typically, the hard X-ray spectrum of the microwave associated
RHESSI microflares can be fit by an isothermal component at low energies
(below 10 or 12 keV) and a nonthermal component at higher energies
(above 12 keV).
Conclusions: .Microflares in hard X-rays and in
microwaves behave like normal flares in many respects. They can have
both thermal and nonthermal components appearing in bremsstrahlung and
gyrosynchrotron radiation.
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Title: Microwave and Hard X ray Imaging of Energetic
Electrons in Solar Flares: Event of 2003 June 17
Authors: Kundu, M. R.; Schmahl, E. J.; White, S. M.
Bibliographic Code: 2006IAUS..233..334K
Abstract
We discuss a large flare that was observed simultaneously by RHESSI in
hard X-rays and by the Nobeyama Radio Heliograph (NoRH) in microwaves.
The imaging observations made both by RHESSI and NoRH show many
interesting features which may be relevant for producing realistic flare
models.
@--------------------------------------------------------------------
Title: RHESSI & Nobeyama Imaging Observations of the X 2.7
Flare of 2003 Nov 3, 00:58 UT
Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.;
White, S. M.
Bibliographic Code: 2005AGUSMSP52A..02K
Abstract
We describe the RHESSI HXR and Nobeyama (NoRH) microwave imaging
observations of an X-class event that was observed during the great
solar activity period of Oct 19--Nov 10, 2003. The flare in question of
class X 2.7 was observed in AR 0488 (position N08W66) on 2003 Nov 3,
00:58:33 UT, with a large peak at 01:15:25 UT, and ending at 03:08:19
UT. The maximum fluxes at 17 and 34 GHz are respectively 678 and 536
SFU. Besides the peak at 01:15 there are two other peaks at approx 01:20
and 01:32:30 UT. In NoRP data the peak at 01:20 is the most dominant at
frequencies 9.40, 3.75, 2.0 GHz. At 1.0 GHz the emission prior to this
peak is fluctuating and a peak with fluctuations exists at around 01:05
UT. The third peak at 01:32:30 UT is spiky and it is nonthermal with a
turnover frequency between 17 and 34 GHz. One significant property of
the HXR emission (below 12 keV) during the period 01:00 - 01:08 is that
the preflare emission, in projection, lies close to and above the
W-limb, although the associated microwave source is on the disk. There
are two preflare sources (RHESSI at 12-25 keV, and NoRH at 17 and 34
Ghz), but it is not clear how they are related. The RHESSI source seems
to coincide in position with the EIT flaring source at its apex. The
morphological structure seems to suggest that we are dealing with a
loop-top HXR source situated at the top of the EIT flaring loop and
flaring sources at 17 and 34 GHz, whose morphology suggests a complex
flaring arcade structure.
@--------------------------------------------------------------------
Title: RHESSI and radio imaging observations of microflares
Authors: Kundu, M. R.; Trottet, G.; Garaimov, V. I.;
Grigis, P. C.; Schmahl, E. J.
Bibliographic Code: 2005AdSpR..35.1778K
Abstract
We present an analysis of five microflares, three observed
simultaneously by RHESSI in hard X-rays and Nobeyama RadioHeliograph
(NoRH) in microwaves (17 GHz) and two observed by RHESSI and Nancay
RadioHeliograph (NRH) at metric wavelengths (150 450 MHz). Since we have
no radio imaging telescopes simultaneously operating at microwave and
meter wavelengths in the same time zone, we are obliged to use a
different set of metric events in contrast to that used for comparison
with the two radio wavelengths. We are interested in using the locations
and other imaging characteristics of the events from both RHESSI and
radio observations instead of just temporal correlation. So we have used
the Nancay (France) metric radioheliograph at 150 450 MHz for this
purpose. Here we describe the properties of five events three in
microwaves and two at metric wavelengths. We discuss the brightness
temperatures, emission measures and the hard X-ray spectral properties
of these microevents. One sees small (mini) flaring loops clearly in
NoRH and RHESSI images. The microwave emission often seems to come from
the RHESSI foot points (for higher energies), and from the entire small
(mini) flaring loop (for lower energies).The RHESSI microflares seem to
be associated in position with metric type III bursts. Frequently, the
hard X-ray spectrum of the microwave associated RHESSI microflares can
be fit by a thermal component at low energies (˜3 12 keV) and a
nonthermal component at higher energies (˜12 20 keV).
@--------------------------------------------------------------------
Title: Multi-wavelength study of a coronal mass ejection: a
flare event from AR\#9393
Authors: Manoharan, P. K.; Kundu, M. R.
Bibliographic Code: 2005AdSpR..35...70M
Abstract
The active region, AR\#9393, produced a number of intense flares during
March-April 2001. In this paper, we report the analysis of an X1.1 flare
event of April 2, 2001 and its associated coronal mass ejection. The
timing and location of the Halpha eruption, radio burst
activities, and the onset of mass ejection suggest an energy release
that occurred close to the surface of the sun. At this region, as shown
by the magnetogram, X-ray and EUV images, the field configuration was
complex and the 3-D extrapolation revealed the presence of a magnetic
null point. Results also suggest that the energy release is followed by
the magnetic reconnection between the low-lying loops near the separator
point and outlying loops. This study provides the support for the
magnetic break-out process to trigger the energy release in eruptive
flare event.
@--------------------------------------------------------------------
Title: The configuration of simple short-duration solar
microwave bursts
Authors: Kundu, M. R.; Nindos, A.; Grechnev, V. V.
Bibliographic Code: 2004A&A...420..351K
Abstract
Using data from the Nobeyama Radioheliograph (NoRH) we study the source
configuration of four simple short-duration 17 and 34 GHz bursts which
have also been observed partially by the Yohkoh Soft X-ray Telescope
(SXT). Two events are consistent with a single flaring loop
configuration. In one of them the flaring loop is resolved in the SXT
images. We derive a self-consistent model for this event by comparing
the radio observations with gyrosynchrotron model loop calculations. Our
best-fit model is able to reproduce both the observed flaring loop shape
as well as the fluxes and structures of the radio emission at the peak
of the event. The flaring loop is relatively small having a footpoint
separation of 16 arcsec and maximum height of 7.7 arcsec. The variation
of the magnetic field along the loop is small (800 G at the footpoints
and 665 G at loop top) and the loop is filled with electrons with
energies up to 10 MeV. The other two bursts show two radio sources; one
source being cospatial with a compact bright soft X-ray loop associated
with a patch of parasitic magnetic polarity whose photospheric magnetic
flux increases before the flares while the other source is not prominent
at any other wavelength range. The two sources are connected with
diffuse loop-like soft X-ray emission. We infer that these bursts
originate from the interaction of two sets of loops with different
sizes. Therefore the simple short duration microwave bursts we studied
do not always appear in the same configuration. Contrary to previous
results not all of them appear as single-loop events. It is possible
that some events are caused by two interacting loops.
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Title: Radio Observations of Rapid Acceleration in a Slow
Filament Eruption/Fast Coronal Mass Ejection Event
Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.;
Manoharan, P. K.; Subramanian, P.;
Ananthakrishnan, S.; Janardhan, P.
Bibliographic Code: 2004ApJ...607..530K
Abstract
We discuss a filament eruption/coronal mass ejection (CME) event
associated with a flare of GOES class M2.8 that occurred on 2001
November 17. This event was observed by the Nobeyama Radio Heliograph
(NoRH) at 17 and 34 GHz. NoRH observed the filament during its eruption
both as a dark feature against the solar disk and a bright feature above
the solar limb. The high cadence of the radio data allows us to follow
the motion of the filament at high time resolution to a height of more
than half a solar radius. The filament eruption shows a very gradual
onset and then a rapid acceleration phase coincident with the launch of
a fast halo CME. Soft X-ray and extreme-ultraviolet (EUV) images show
heating in a long loop underneath the filament prior to the flare. The
NoRH height-time plot of the filament shows a roughly constant gradual
acceleration for 1 hr, followed by a very abrupt acceleration coincident
with the impulsive phase of the associated flare, and then a phase of
constant velocity or much slower acceleration. This pattern is identical
to that recently found to occur in the motion of flare-associated CMEs,
which also show a sharp acceleration phase closely tied to the impulsive
phase of the flare. When the rapid acceleration occurs in this event,
the flare site and the filament are separated by ~0.5 Rsolar,
making it unlikely that a disturbance propagates from one location to
the other. Models in which a disruption of the large-scale coronal
magnetic field simultaneously permits the acceleration of the filament
and the flare energy release seem to be a better explanation for this
event.
@--------------------------------------------------------------------
Title: RHESSI and Microwave Imaging Observations of Two
Solar Flares
Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.
Bibliographic Code: 2004AAS...204.5402K
Abstract
We present hard X-ray (RHESSI) and microwave (NoRH) imaging observations
of two solar flares of M-class observed on March 14 and March 12 of
2002, one located near the disk center and the other near the E-limb.
For the March 14 event (near disk center), both hard X-ray and microwave
observations indicate that the flaring region consisted of a complex of
multiple loops. In microwaves its spatial configuration has a
double-loop structure; at the main flare site (primary flaring loop) we
observe microwave, HXR, EUV emissions and at a remote site (connected to
main site by a long loop) we observe microwaves only due to a strong
magnetic field. Some HXR foot point sources (in 25-100 KeV bands) have
co-located microwave footpoint sources. The hard X-ray spectrum can be
fitted with a thick target model with a thermal component and a broken
power-law component. The March 12 E-limb event was fully observed by
Nobeyama Radio Heliograph (NoRH), but in hard X-rays it was observed
only from around the peak until the end of flare, because of RHESSI
night time. In hard X-rays (6-50 KeV) it was clearly a coronal source
located above an EIT loop, and it seems to have significant motion in
the post flare period. In microwaves it was also a coronal source in
both 17 and 34 GHz. Due to the relatively poor resolution of NoRH, the
overall source size in radio is large, encompassing the RHESSI source at
the start and end of its motion. The spatial maximum of the 17 GHz
source appears at a coronal height below the HXR source. The microwave
source also shows motion, along with the expansion of the EIT flaring
loop. The hard-ray spectral properties of the flare will be discussed.
@--------------------------------------------------------------------
Title: Nobeyama Radioheliograph and RHESSI Observations of
the X1.5 Flare of 2002 April 21
Authors: Kundu, M. R.; Garaimov, V. I.; White, S. M.;
Krucker, S.
Bibliographic Code: 2004ApJ...600.1052K
Abstract
We present an overview of the radio observations of the X1.5 flare of
2002 April 21 and complementary data from other wavelengths. This flare
was fairly well observed by the Ramaty High Energy Spectroscopic Imager
(RHESSI) spacecraft and fully observed by the Nobeyama Radioheliograph
(NoRH) at 17 and 34 GHz. This long-duration event lasted more than 2 hr
and featured a beautiful arcade of rising loops on the limb visible at
X-ray, EUV, and radio wavelengths. The main flare was preceded by a
small event 90 minutes earlier showing a long EUV loop connecting
well-separated radio and hard X-ray sources. The main flare itself
starts with a compact radio and hard X-ray source at the eastern end of
the region that develops into emission close to the solar surface (and
well inside the solar limb) over a large region to the northwest. As the
flare proceeds, a large set of loops is seen to rise well above the
solar limb. Distinct regions of radio emission with very different time
behavior can be identified in the radio images, and, in particular, a
peculiar nonthermal source seen in radio and hard X-rays low in the
corona at the base of the arcade is seen to turn on 30 minutes after the
start of the impulsive phase. At about the same time, an extremely
intense burst of coherent radio emission is seen from 500 to 2000 MHz;
we speculate that this lower-frequency burst is produced by electrons
that are accelerated in the nonthermal source at the base of the arcade
and injected into the loop system where they radiate plasma emission in
the 1010 cm-3 density plasma at the top of the
arcade of loops. This event is striking as a demonstration of the many
ways in which a flare can produce radio emission, and the combined data
at different wavelengths reveal a diversity of energy release and
nonthermal acceleration sites.
@--------------------------------------------------------------------
Title: RHESSI and Microwave Imaging Observations of Two
Solar Flares
Authors: Kundu, M. R.; Schmahl, E. J.; Garaimov, V. I.
Bibliographic Code: 2004IAUS..223..425K
Abstract
We describe two flares of GOES class M5.7 and 1.5 which were observed
simultaneously by RHESSI (Ramaty High Energy Solar Spectroscopic Imager)
and NoRH (Nobeyama Radio Heliograph). Both flares exhibit slow motions
suggestive of changing magnetic shear, loop expansion, or gradual
reconnection. One flare is clearly a coronal hard X-ray and microwave
flare.
@--------------------------------------------------------------------
Title: Giant Meterwave Radio Telescope observations of an
M2.8 flare: Insights into the initiation of a
flare-coronal mass ejection event
Authors: Subramanian, Prasad; Ananthakrishnan, S.;
Janardhan, P.; Kundu, M. R.; White, S. M.;
Garaimov, V. I.
Bibliographic Code: 2003SoPh..218..247S, eprint = astro-ph/0309661
Abstract
We present the first observations of a solar flare with the GMRT. An
M2.8 flare observed at 1060 MHz with the GMRT on 17 November 2001 was
associated with a prominence eruption observed at 17 GHz by the Nobeyama
radioheliograph and the initiation of a fast partial halo CME observed
with the LASCO C2 coronagraph. Towards the start of the eruption, we
find evidence for reconnection above the prominence. Subsequently, we
find evidence for rapid growth of a verticurrent sheet below the
erupting arcade, which is accompanied by the flare and prominence
eruption.
@--------------------------------------------------------------------
Title: Radio Observations of Rapid Acceleration in a Slow
Filament Eruption/Fast CME Event
Authors: Kundu, M. R.; White, S. M.; Garaimov, V. I.;
Manoharan, P. K.; Subramanian, P.;
Ananthakrishnan, S.; Janardhan, P.
Bibliographic Code: 2003AGUFMSH21A..06K
Abstract
We discuss a filament eruption/coronal mass ejection (CME) associated
flare event of GOES class M2.8 that occurred on November 17, 2001. This
event was observed simultaneously by Nobeyama RadioHeliograph (NoRH) at
17 and 34 GHz and by the Giant Meterwave Radio Telescope (GMRT) in India
at 1060 MHz. The flare occurred in active region 9704 at S18E41. NoRH
observes the filament during its eruption both as a dark feature against
the solar disk and a bright feature above the solar limb. The filament
eruption shows a very gradual onset and then a rapid acceleration phase
coincident with the launch of a fast halo CME. The flare on the disk in
microwaves has a gradual rise, a broad maximum and a gradual decay. At
1060 MHz, its time profile had three impulsive peaks. The NoRH
height--time plot of the filament shows a roughly constant gradual
acceleration for an hour, followed by a very abrupt acceleration
coincident with the impulsive phase of the associated flare. Soft X-ray
images show heating in a long loop underneath the filament prior to the
flare. The impulsive behavior of 1060 MHz emission combined with high
brightness temperatures indicated the existence of nonthermal electrons
in loops that clearly are not the same as the loops containing the
microwave-emitting electrons. The latter are dominated by thermal
bremsstrahlung and agree well with the EUV and soft X-ray loops. This
study is consistent with recent findings that the rapid acceleration of
flare--associated CMEs is closely tied to the impulsive phase of the
flare. A trigger is required to cause the rapid acceleration to occur at
the same time as the flare even though the two events are spatially well
separated. We speculate that this trigger is provided by some kind of
reconnection in the multiple flux systems that exist between the flaring
active region and the erupting filament.
@--------------------------------------------------------------------
Title: Radio and Hard X-Ray Images of High-Energy Electrons
in an X-Class Solar Flare
Authors: White, S. M.; Krucker, S.; Shibasaki, K.;
Yokoyama, T.; Shimojo, M.; Kundu, M. R.
Bibliographic Code: 2003ApJ...595L.111W
Abstract
We present the first comparison between radio images of high-energy
electrons accelerated by a solar flare and images of hard X-rays
produced by the same electrons at photon energies above 100 keV. The
images indicate that the high-energy X-rays originate at the footpoints
of the loops dominating the radio emission. The radio and hard X-ray
light curves match each other well and are quantitatively consistent
with an origin in a single population of nonthermal electrons with a
power-law index of around 4.5-5. The high-frequency radio spectral index
suggests a flatter energy spectrum, but this is ruled out by the X-ray
spectrum up to 8 MeV. The preflare radio images show a large hot
long-lived loop not visible at other wavelengths. Flare radio brightness
temperatures exceed 109 K, and the peak in the radio spectrum
is as high as 35 GHz: both these two features and the hard X-ray data
require very high densities of nonthermal electrons, possibly as high as
1010 cm-3 above 20 keV at the peak of the flare.
@--------------------------------------------------------------------
Title: Coronal Structure of a Flaring Region and Associated
Coronal Mass Ejection
Authors: Manoharan, P. K.; Kundu, M. R.
Bibliographic Code: 2003ApJ...592..597M
Abstract
We report the multiwavelength investigations of an eruptive flare event
that occurred on 2001 April 2 at about 11 UT. The manifestations
associated with this flare event have been studied from the near-Sun
region to about 0.5 AU. The Halpha images from the Meudon
Spectroheliograph reveal a fast spectacular eruption of plasmoids from
the flare site to the west and a Moreton wave disturbance propagating
toward the south. A bright, fast, wide coronal mass ejection (CME)
associated with this eruptive event was imaged by SOHO/LASCO and the
remote-sensing interplanetary scintillation technique. The radio
measurements from the Nançay Radioheliograph and Tremsdorf Radio
Telescope have been useful in identifying the radio signatures of the
CME's initiation. The metric type II radio bursts produced at the time
of CME onset also propagate toward the west, and their positions
coincide with the magnetic null point, which was located at the
southwest part of NOAA active region 9393. The timings and positions of
the radio bursts, the Halpha eruption, and the CME onset as well as
the magnetic field configuration suggest a release of energy at the null
point, and as indicated by the Moreton wave, the eruption starts close
to the chromospheric or low coronal level. The results support the
``breakout'' scenario proposed by S. Antiochos and coworkers, and they
are also suggestive that the energy release is followed by magnetic
reconnection between the low-lying loops near the separatrix and the
loop system above them.
@--------------------------------------------------------------------
Title: Nobeyama Radio Heliograph and RHESSI Observations of
the X1.5 Flare of April 21, 2002
Authors: Kundu, M. R.; Garaimov, V. I.; White, S. M.;
Krucker, S.
Bibliographic Code: 2003SPD....34.1812K
Abstract
We present radio observations of the X1.5 flare of April 21, 2002, and
complementary data from other wavelengths. This flare was fairly well
observed by the spacecraft RHESSI and fully observed by the Nobeyama
Radio Heliograph at 17 and 34 GHz. This long-duration event lasted more
than 2 hours and features a beautful arcade of rising loops on the limb
visible at X-ray, EUV and radio wavelengths. The main flare was preceded
by a small event 90 minutes earlier showing a long EUV loop connecting
well-separated radio and hard X-ray sources. The main flare itself
starts with a compact radio and hard X-ray source at the eastern end of
the region that is followed by emission close to the solar surface (well
inside the solar limb) over a large region to the northwest. As the
flare proceeds a large set of loops is seen to rise well above the solar
limb. Distinct regions of radio emission with very different time
behaviour can be identified in the radio images, and in particular a
peculiar nonthermal 17 GHz source low in the corona at the base of the
arcade is seen to turn on 30 minutes after the start of the impulsive
phase. At about the same time an extremely intense burst of coherent
radio emission is seen from 500 to 2000 MHz: we speculate that this
lower-frequency burst is located at the top of the arcade of loops.
@--------------------------------------------------------------------
Title: RHESSI and Microwave Imaging Observations of Two
Microflares
Authors: Garaimov, V. I.; Kundu, M. R.; Grigis, P. C.
Bibliographic Code: 2003SPD....34.1603G
Abstract
We describe two microflares which occurred in the AR 9934 at 03:58 UT
May 3, 2002 and at 05:08 UT May 4, 2002. AR 9934 was a complex region
which contained a sunspot with a strong negative polarity of the
magnetic field on the north side and a bipolar region on the south side.
Analysis of the MDI images shows fast evolution of the south part of the
region. TRACE images show many small loops in the south part of AR and
the complex loop which connected the north sunspot to the south side of
the region. We have observations of both of these events by Nobeyama
Radio Heliograph and RHESSI. The NoRH 17 GHz maps show loop like
structure of the radio source which has a maximum above the sunspot land
it connects to the south side of AR. RHESSI maps superimposed on the
NoRH maps show that X-ray emission in the range 3-25 keV are located
inside the radio contours. During both events hard X-ray emission was
located in the south part of the AR. RHESSI maps corresponding to the
maximum X-ray emission during the event of May 3, 2002 clearly show an
X-ray loop in the range 3-6 keV and two footpoints of the loop in the
6-12 and 12-25 keV ranges. These footpoints are located above opposite
magnetic polarities as seen in overlays of hard X-ray images on the MDI
image. Also hard X-ray emission seems to be brighter from the northern
footpoint than from the other. The hard X-ray images of the event of May
4, 2002 shows a small X-ray loop (smaller than size of the loop in the
previous event), located close to the same position relative to the
active region. We calculated the hard X-ray spectrum, temperature and
emission measure for both events.
@--------------------------------------------------------------------
Title: Quasi-periodic Pulsations in a Solar Microwave Burst
Authors: Grechnev, V. V.; White, S. M.; Kundu, M. R.
Bibliographic Code: 2003ApJ...588.1163G
Abstract
Quasi-periodic pulsations in solar flares can provide important
information on physical conditions in flaring regions. In this paper, we
study a microwave burst that showed deep quasi-periodic pulsations. The
most dramatic feature of this event has been discussed by Asai and
coworkers. In the second of four bursts during the flare, strongly
modulated pulsations appear in radio images from the eastern end of a
long loop and in hard X-rays from the western end of the loop. We show,
in addition, that (1) at least five distinct radio sources with very
different time profiles can be identified, including emission from the
long loop connecting the modulated radio and X-ray sources; (2)
substructure is also present in the radio emission from the eastern end
of the long loop during the first burst of the flare, but with
timescales shorter than in the second burst; (3) radio modulations are
seen at the western end of the loop during the second burst but at a
level some 20 times weaker than at the eastern end; (4) these radio
modulations at the western end of the loop, like the hard X-ray
modulations at the same location, appear to lead the modulations at the
eastern end by about 0.5 s, but all have the same period. The period of
the modulation can be explained by MHD oscillations of the loop ~120"
long connecting the sources: both oscillations that change the magnetic
field strength in the loop, such as propagating fast-mode waves, and
torsional oscillations that change the direction of the magnetic field
in the loop can explain the observed properties of the modulation of the
radio emission. An impulsive reconnection episode is a plausible source
of oscillating fast-mode waves and is consistent with some other aspects
of the event. However, it is difficult to reconcile the strength of the
radio modulations at the eastern end of the loop with their delay
relative to the emissions at the western end, where the modulation is
observed to be much weaker. If the electrons originate at the western
end where the main energy release seems to occur, and the modulation is
imposed on them there before they propagate 1010 cm to the
other end of the loop, any effects due to a spread in electron energies
or pitch angles would lead to a spread in propagation times that should
smooth out the modulation of the radio emission from the remote source,
as should any trapping of electrons in the loop: yet the radio emission
from the eastern end of the loop shows much stronger modulation than the
radio and hard X-ray emission from the western end of the loop.
@--------------------------------------------------------------------
Title: Radio observations of explosive energy releases on
the Sun
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 2003dysu.book..288K
Abstract
This chapter is devoted to a discussion of the radio observations of
explosive energy releases (normal flares and small-scale energy
releases) on the Sun. Radio imaging observations of solar flares and
coronal transients and the relationship of radio phenomena with those
observed in hard and soft X-rays, and underlying physics are discussed.
@--------------------------------------------------------------------
Title: Distinctive spatial configuration of a class of
microwave flaring sources
Authors: Kundu, M. R.; Garaimov, V. I.
Bibliographic Code: 2003AdSpR..32.2497K
Abstract
We discuss a class of microwave flares whose source regions exhibit a
distinctive spatial configuration; the primaryenergy release in these
flares results from the interaction between emerging magnetic flux and
an existing overlying region. Such events typically exhibit radio, X-ray
and EUV emission at the main flare site (the site of interaction) and in
addition radio emission at a remote site up to 1 × 105
km away in another active region. We have identified and studied more
than a dozen microwave flares in this class, in order to arrive at some
general conclusions on reconnection and energy release in such solar
flares. Typically, these flares show a gradual rise showing many
subsidiary peaks in both radio and hard X-ray light curves with a
quasi-oscillatory nature with periods of 5 6 seconds, a bright compact
X-ray & EUV emitting loop in the main flare source, a delay of the
radio emission from the remote source relative to the main
X-ray-emitting source. The magnetic field in the main flare site changes
sharply at the time of the flare, and the remote site appears to be
magnetically connected to the main flare site.
@--------------------------------------------------------------------
Title: Distinctive spatial configuration of a class of
microwave flaring sources
Authors: Kundu, M. R.; Garaimov, V. I.
Bibliographic Code: 2002ESASP.506..319K
Abstract
We discuss a particular spatial configuration of a class of microwave
flaring regions in which the primary energy release results from the
interaction between emerging magnetic flux and an existing overlying
region. Such events typically exhibit radio and X-ray emission at the
main flare site (the site of interaction) and in addition radio emission
at a remote site up to 1×105 km away in another active
region. We have identified and studied more than a dozen microwave
flares in this class, in order to arrive at some general conclusions on
reconnection and energy release in such solar flares.
@--------------------------------------------------------------------
Title: The Physical Properties of a Flaring Loop
Authors: White, S. M.; Kundu, M. R.; Garaimov, V. I.;
Yokoyama, T.; Sato, J.
Bibliographic Code: 2002ApJ...576..505W
Abstract
We use high-resolution radio observations to study the physical
parameters of a flaring loop. The loop is visible at radio wavelengths
because of gyrosynchrotron emission by nonthermal electrons (energies
typically above several hundred keV) accelerated by the flare. We are
able to measure the loop thickness and length with a precision on the
order of 1". We find that the loop length increases from about 60"
initially to about 80" in the decay phase of the event. The loop
(averaged along its length) initially is no more than 3" wide. The soft
and hard X-ray data obtained with the Soft X-Ray Telescope and Hard
X-Ray Telescope on the Yohkoh satellite are consistent with the same
loop as observed at radio wavelengths (although the soft X-ray
morphology has some small differences early in the event). This event
was accompanied by a coronal mass ejection and a coronal dimming visible
in Solar and Heliospheric Observatory Extreme-Ultraviolet Imaging
Telescope images, so it involved a very large volume of the corona, yet
the radio observations clearly indicate that much of the energy release
in the low corona was restricted to a region apparently no more than
2000 km across. As the event proceeds, the loop develops a bright
feature at the loop top in both the radio and soft X-ray images that
cannot be reproduced in gyrosynchrotron loop models in which the
electron distribution has relaxed by pitch angle scattering to fill the
loop. This prevents us from using the flare properties to measure the
magnetic field strength and variation along the loop. The bright
loop-top source may require that trapping of electrons take place at the
loop top late in the event.
@--------------------------------------------------------------------
Title: Multiple-loop structure of a solar flare from
Microwave, EUV and X-ray Imaging Data
Authors: Garaimov, V. I.; Kundu, M. R.
Bibliographic Code: 2002SoPh..207..355G
Abstract
We present the results of an analysis of a flare event of importance
M2.8 that occurred at 00:56 UT 28 August 1999. The analysis is based
upon observations made with the Nobeyama radioheliograph (NoRH) and
polarimeters (NoRP), TRACE, SOHO/MDI, EIT, and Yohkoh/SXT. The images
show a very complex flaring region. Pre-flare TRACE and EIT images at
00:24 UT show a small brightening in the region before the flare
occurred. The active region in which the flare occurred had evolving
magnetic fields, and new magnetic flux seems to have emerged. The X-ray
and radio time profiles for this event show a double-peaked structure.
The polarimeter data showed that the maximum radio emission (1200
s.f.u.) occurred at 9.4 GHz. At 17 GHz the NoRH images appear to show
four different radio sources including the main spot and the main flare
loop. Most of the microwave emission seems to originate from the main
flare loop. Comparison of BATSE and microwave time profiles at 17 and 34
GHz from the main sunspot source shows that these profiles have similar
structures and they coincide with the hard X-ray peaks. The maximum of
the flare loop emission was delayed by 10 s relative to the second
maximum of the sunspot associated flare emission. Analysis of SXT images
during the post-flare phase shows a complex morphology - several
intersecting loops and changes in the shape of the main flare loop.
@--------------------------------------------------------------------
Title: Multiwavelength Study of a Coronal Mass Ejection:
Eruption from AR\#9393
Authors: Manoharan, P. K.; Kundu, M. R.
Bibliographic Code: 2002AAS...200.3610M
Abstract
We report the investigation of one of the coronal mass ejections
unleashed by the largest active region, AR9393, of the current solar
cycle. This mass ejection was associated with an X1.1 flare that
occurred on April 2, 2001 at about 11 UT and also showed small effect in
terms of energetic particle. The analysis of H-alpha images obtained
from the Meudon spectroheliograph shows a fast eruption towards the
north-west direction and wave-like propagation from the eruption site.
The acceleration of the ejecta results in a speed of about 150-200 km/s
close to the disk. The associated radio emission observed with the
Nancay Radioheliograph in the frequency range 160-327 MHz shows radio
emitting regions moving towards north with time and with increasing
wavelength. The mass ejection observed with the coronagraphs on board
LASCO/ SOHO is consistent with the eruption seen in the H-alpha. We
discuss the formation and morphology of the ejection and its
interplanetary consequences.
@--------------------------------------------------------------------
Title: Multiple-Loop Structure of a Solar Flare from
Microwave, EUV and X-Ray Imaging Data
Authors: Garaimov, V. I.; Kundu, M. R.
Bibliographic Code: 2002mwoc.conf..233G
Abstract
We present the results of analysis of a flare event of importance M2.8
that occurred at 00:56 UT Aug 28, 1999. The analysis is based upon
observations made with the Nobeyama Radio Heliograph(NoRH) and
Polarimeters(NoRP), TRACE, SOHO/MDI,EIT and Yohkoh/SXT. MDI, TRACE, EIT,
Soft X-ray and radio images show a very complex structure of the flaring
region. Pre-flare TRACE and EIT images at 00:24UT show a small
brightening in the region before the flare occurred. The active region
in which the flare occurred had changing magnetic fields, and a new
magnetic flux seems to have emerged. The X-Ray and radio time profiles
for this event show a double peaked structure. The polarimeter data
showed that the maximum radio emission (1200sfu) occurred at 9.4 GHz. At
17GHz there appears to be four different radio sources including the
main spot and the main flare loop. Most of the microwave emission seems
to originate from the main flare loop. Comparison of BATSE and microwave
time profiles at 17 and 34GHz from the main sunspot source shows that
these profiles have similar structures and they coincide with the Hard
X-ray peaks. The maximum of the flare loop emission was delayed by 10
sec relative to the second maximum of the sunspot associated flare
emission. Analysis of SXT images during the post-flare phase shows a
complex morphology - several intersecting loops and changes in the shape
of the main flare loop. Implications of the complex morphology of both
radio and X-ray flaring sources will be discussed.
@--------------------------------------------------------------------
Title: Double Loop Configuration of a Flaring Region from
Microwave, Extreme-Ultraviolet, and X-Ray Imaging
Data
Authors: Kundu, M. R.; Grechnev, V. V.; Garaimov, V. I.;
White, S. M.
Bibliographic Code: 2001ApJ...563..389K
Abstract
We use extensive multiwavelength data to study a flare belonging to the
interacting-loop class of events identified by Hanaoka. The class of
flares is identified morphologically from the presence of two
well-separated radio sources in 17 GHz images (in this event, 160"
apart), with only one source showing soft X-ray emission. This event
shows many of the other properties apparently shared by this class of
flares: a gradual rise showing many subsidiary peaks in both radio and
hard X-ray light curves with a quasi-oscillatory nature, the presence of
a bright compact X-ray-emitting loop in the main flare source, a delay
of the radio emission from the remote source relative to the main
X-ray-emitting source, higher circular polarization in the radio
emission of the remote source than in the main source, and stronger
photospheric magnetic field in the remote source. The new results of our
analysis are that we are able to show, using a sequence of magnetograms,
that the magnetic field in the main flare site changes sharply at the
time of the flare, and further we argue that the remote site is
magnetically connected to the main flare site only up to the time of the
main impulsive phase, at which point we believe the magnetic connection
to the remote site was broken and further flare manifestations are
largely confined to the main flare site. This severing of the magnetic
connection between two well-separated active regions may be an intrinsic
part of the energy release in this flare. The region around the main
flare site also exhibits rotation in the magnetogram in the period
leading up to the flare. Radio and hard X-ray oscillations with periods
of order 5-10 s are observed in the rise phase of this event. If they
are due to transverse oscillations of the flare loop at the
Alfvén speed, then the density in the loop is inferred to be of
order 1011 cm-3 and to increase with time as
expected.
@--------------------------------------------------------------------
Title: Reconciling Extreme-Ultraviolet and Radio
Observations of the Sun's Corona
Authors: Zhang, J.; Kundu, M. R.; White, S. M.; Dere, K. P.;
Newmark, J. S.
Bibliographic Code: 2001ApJ...561..396Z
Abstract
The Sun's corona, which is composed of plasma at a temperature of a few
millions of degrees, can be best viewed in two electromagnetic domains,
one from wavelengths of a few angstroms to hundreds of angstroms (in the
soft X-ray and EUV domain), the other from wavelengths of a few
centimeters to several tens of centimeters (in the radio domain). In
this paper, we present a quantitative comparison of coronal observations
made in these two domains with high spatial resolution over the full
disk of the Sun. The EUV observations were taken with the EIT
(Extreme-Ultraviolet Imaging Telescope) on board SOHO (Solar and
Heliospheric Observatory), and the radio observations were taken with
the VLA (Very Large Array). The two sets of images show very similar
morphologies, indicating that the different wavelengths originate from
common solar features. We predict radio fluxes using the temperature and
emission measure of the corona calculated from EIT observations,
adopting Meyer's table of coronal abundances for the calculations. In
each of the seven observations investigated, there always exists a good
linear correlation in the pixel-by-pixel correlation plot between the
predicted and the observed radio flux for coronal features over a wide
range of flux variation. Nevertheless, the predicted radio flux is
systematically larger than that observed by a factor of 2.0+/-0.2, on
average. We attribute the difference to the underestimation of the
abundance of Fe relative to H in the abundances adopted by Meyer. On
this basis, we place the absolute Fe abundance in the corona at
7.8×10-5, which has an enrichment factor of 2.4
relative to the accepted photospheric Fe abundance.
@--------------------------------------------------------------------
Title: On the Temporal Relationship between Coronal Mass
Ejections and Flares
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.;
White, S. M.
Bibliographic Code: 2001ApJ...559..452Z
Abstract
The temporal relationship between coronal mass ejections (CMEs) and
associated solar flares is of great importance to understanding the
origin of CMEs, but it has been difficult to study owing to the nature
of CME detection. In this paper, we investigate this issue using the
Large Angle and Spectrometric Coronagraph and the EUV Imaging Telescope
observations combined with GOES soft X-ray observations. We present four
well-observed events whose source regions are close to the limb such
that we are able to directly measure the CMEs' initial evolution in the
low corona (~1-3 Rsolar) without any extrapolation; this
height range was not available in previous space-based coronagraph
observations. The velocity-time profiles show that kinematic evolution
of three of the four CMEs can be described in a three-phase scenario:
the initiation phase, impulsive acceleration phase, and propagation
phase. The initiation phase is characterized by a slow ascension with a
speed less than 80 km s-1 for a period of tens of minutes.
The initiation phase always occurs before the onset of the associated
flare. Following the initiation phase, the CMEs display an impulsive
acceleration phase that coincides very well with the flares' rise phase
lasting for a few to tens of minutes. The acceleration of CMEs ceases
near the peak time of the soft X-ray flares. The CMEs then undergo a
propagation phase, which is characterized by a constant speed or slowly
decreasing in speed. The acceleration rates in the impulsive
acceleration phase are in the range of 100-500 m s-2. One CME
(on 1997 November 6, associated with an X9.4 flare) does not show an
initiation phase. It has an extremely large acceleration rate of 7300 m
s-2. The possible causes of CME initiation and acceleration
in connection with flares are explored.
@--------------------------------------------------------------------
Title: Metric Radio Emission Associated with X-Ray Plasmoid
Ejections
Authors: Kundu, M. R.; Nindos, A.; Vilmer, N.; Klein, K.-L.;
Shibata, K.; Ohyama, M.
Bibliographic Code: 2001ApJ...559..443K
Abstract
In this paper we report the first detection of metric/decimetric radio
emission associated with two soft X-ray plasmoid ejecta events that
occurred during two limb flares observed by the Yohkoh SXT. In the first
event a loop started to rise slowly (~10 km s-1) before the
beginning of the hard X-ray impulsive phase of the flare. At about the
onset of the impulsive flare, there was acceleration of the ejecta,
resulting in a speed of 130 km s-1 and finally to ~200 km
s-1. The associated radio emission was observed with the
Nançay radioheliograph (NRH) in the frequency range of 230-450
MHz. It was an unpolarized continuum that lasted 8-10 minutes. The 410
MHz source was located close to the height where the plasmoid was last
identified in the SXT images. In the second event an eruption resulted
in the expansion of a large-scale, looplike feature and the development
of two plasmoid ejecta which moved in different directions. The speed of
the ejecta was 60-100 km s-1. In this event, the associated
radio emission was a long-lasting (about 2 hr) continuum observed from
450 to 164 MHz. The onset of the low-frequency emission was delayed with
respect to the onset of the high-frequency emission. In both cases the
radio sources were located above the soft X-ray ejecta in the general
direction of the prolongation of the ejecta movement. In both cases the
radio emission comes from nonthermal electrons which are accelerated in
close relationship with the propagation of the X-ray plasmoid: as the
plasmoid reaches higher altitudes, it interacts with increasingly more
extended magnetic field lines and new coronal sites of production of
nonthermal electrons are created.
@--------------------------------------------------------------------
Title: A Multiwavelength Study of Three Solar Flares
Authors: Kundu, M. R.; Nindos, A.; White, S. M.;
Grechnev, V. V.
Bibliographic Code: 2001ApJ...557..880K
Abstract
In this paper we seek a self-consistent model for three strong limb
flares observed at 17 and 34 GHz by the Nobeyama radioheliograph and
also in soft X-rays and hard X-rays by the Yohkoh SXT (Soft X-Ray
Telescope) and HXT (Hard X-Ray Telescope) instruments. Additional radio
spectral data were provided by the Nobeyama polarimeter. The flare
geometry is simple, with one well-defined flaring loop in each event.
The 17 and 34 GHz emissions are optically thin gyrosynchrotron radiation
from energetic electrons that outlines the flaring loops and peaks close
to the loop tops. We infer that the variation of magnetic field along
the loops is very small. We try to reproduce the observed radio
morphologies and fluxes using a model gyrosynchrotron loop. The results
of our modeling rely on the model magnetic field geometry that we
choose. Although the exact loop geometry cannot be constrained from a
two-dimensional snapshot, we choose for simplicity a line-dipole
magnetic field, and the model field lines are circular. The SXT/HXT
images are used to provide the physical parameters of the model loops.
The high-frequency polarimeter data give the energy spectral index of
the radio-emitting electrons. We could not reconcile the observed radio
morphologies and fluxes using classic dipole magnetic field models. The
best-fit model that uses the same input parameters for both frequencies
and partly reconciles the observed 17 and 34 GHz morphologies and fluxes
is produced when we invoke a magnetic field with constant strength along
the model loop. These model loops have uniform thickness. The derived
densities of the radio-emitting electrons are (1-6)×104
cm-3 with energy limits between 60 and 5000 keV. These models
are the best fits we can get under the best assumptions we can justify,
but they do not in fact match the radio morphologies very well; their
problems and limitations are discussed.
@--------------------------------------------------------------------
Title: Seemingly intersecting flaring loops in microwaves:
Possible radio evidence for reconnection
Authors: Kundu, M. R.; Grechnev, V. V.
Bibliographic Code: 2001EP&S...53..585K
Abstract
We present possible radio evidence of magnetic reconnection in a solar
flare -- an LDE event of GOES class M3.2 that was observed on 1999
February 16 on the disk. Our evidence is based upon the facts that we
observed a bright microwave source-blob at 17 and 34 GHz near the
intersection of two seemingly intersecting flaring loops or as a
loop-top source above one flaring loop. The bright microwave source is
clearly non-thermal and its time profile is similar to those of the
flaring footpoint microwave sources; and in the late decay phase of the
event the microwave source structure is similar to that of the
corresponding SXR source.
@--------------------------------------------------------------------
Title: Intersecting Flaring Loops in Microwaves: Possible
Radio Evidence for Magnetic Reconnection
Authors: Kundu, M. R.; Grechnev, V. V.
Bibliographic Code: 2001AGUSM..SP51A05K
Abstract
We present possible radio evidence of magnetic reconnection in a solar
flare - an LDE event of GOES class M3.2 that was observed on 1999
February 16 on the disk. Our evidence is based upon the facts that we
observed a bright microwave source - a bright blob at 17 and 34~GHz near
the intersection of two apparently intersecting flaring loops or as a
loop-top source above one flaring loop. The bright microwave source is
clearly nonthermal and its time profile is similar to those of the
flaring footpoint microwave sources, and in the late decay phase of the
event the microwave source structure is similar to that of the
corresponding SXR source. The loop-top microwave source shows a movement
of order 10 km/s, similar to that observed by Yohkoh in soft X-rays in
one LDE event which was considered to be a reconnection event. It is
important to note that in the late decay phase this event was associated
with CGRO/BATSE 100-300 keV energy electrons which appear to originate
primarily from the footpoints of one flaring loop. There are data
available in Halpha from Hida observatory in Japan which show an
ejection during this apparent reconnection event.
@--------------------------------------------------------------------
Title: Double Loop Configuration of a Flaring Region from
Microwave, EUV and X-ray Imaging Data
Authors: Garaimov, V. I.; Kundu, M. R.; Grechnev, V. V.;
White, S. M.
Bibliographic Code: 2001AGUSM..SP51A04G
Abstract
We present the results of a study of a flare of importance M1.7 that was
observed with the Nobeyama Radio Heliograph (NoRH), SOHO/EIT and MDI and
Yohkoh/HXT & SXT. The flare ocurred in a complex of two active
regions AR~8741 and AR~8739, which were separated by ~ 3 arc min. The
main flaring region was AR~8741, which consisted of two compact
oppositely polarized components as judged by MDI magnetogram data.
17~GHz and 34~GHz microwave emissions as well as EUV, and hard and soft
X-ray emissions from the flare originated primarily from the vicinity of
the compact components of opposite polarity in AR~8741. There was some
17~GHz flaring emission from AR~8739. Clearly, we are dealing with a
large magnetic loop connecting AR~8741 and AR~8739, as well as a compact
loop in AR~8741 which was the main flare site. One of the magnetic
components of the compact loop increased in field strength approximately
1 hour prior to the flare onset. MDI magnetograms showed some other
changes in the magnetic fields associated with the compact loop. We
suggest that the interaction of the compact loop with the large loop was
responsible for causing the flare. The radio source structures at 17 and
34 GHz along with EUV, hard and soft X-ray source structures of the
flaring region will be presented.
@--------------------------------------------------------------------
Title: The Physical Properties of a Flaring Coronal Loop
Authors: White, S. M.; Kundu, M. R.; Garaimov, V. I.;
Yokoyama, T.
Bibliographic Code: 2001AGUSM..SP42A06W
Abstract
We present high resolution radio and X-ray images of emission from
nonthermal electrons trapped in a flaring coronal loop and measure
various physical properties of the loop, including the loop thickness as
a function of position along the loop and intensity profiles along the
loop. Gyrosynchrotron modelling provides a complementary method for
inferring parameters such as the magnetic field variation along the
loop, and we compare the results of the two approaches. Both agree that
there is little variation in magnetic field strength along the loop;
this purely radio measurement thus supports the same inference derived
from measurements of EUV and X-ray loop thicknesses.
@--------------------------------------------------------------------
Title: A Radio Study of the Evolution of Spatial Structure
of an Active Region and Flare Productivity
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.;
Raulin, J.-P.
Bibliographic Code: 2001ApJS..133..467K
Abstract
We present the results of a radio study of the evolution of an active
region through its flare productivity. The radio study was carried out
with data obtained by the Nobeyama Radio Heliograph at 17 GHz. We chose
the active region AR 7515, which appeared at the east limb on 1993 May
23 and then evolved during its passage across the disk. We followed its
evolution until June 2. This region produced many small flares. We
consider this region to be a typical active region in the sense that it
did not produce any large flares, but a large number of weak flares. We
investigate the optical and magnetic development of the region and show
how this affects the locations of the flaring activity. We discuss a
number of events in detail in order to investigate the roles of
nonthermal and thermal radio emission in the flares. The nonthermal
gyrosynchrotron emission generally occurs in regions of strong magnetic
fields, is generally circularly polarized, and often varies rapidly in
time. On the other hand, gradual radio components tend to be thermal and
only weakly polarized, if at all. An interesting aspect of evolution of
the flares in this region is that many of the flares in the early phase
of the evolution show strong but brief nonthermal radio emission in the
impulsive phase followed by gradual thermal emission, whereas in the
last 3 days more gradual events without a strong spike of radio emission
in the impulsive phase tend to be seen. Correspondingly, the flare
images suggest that the radio sources are more compact during the early
phases and more extended in the last half of the period covered. The
most dominant component of the preflare region is often not the
component that undergoes immediate flaring. Sometimes a number of
components in the preflare region participate in the flare process
together. We speculate that these component sources are unresolved
compact bipolar loops that flare in sequence. Loop-loop interactions
occurring at many different sites at the same time seems to be a less
plausible explanation of these events.
@--------------------------------------------------------------------
Title: Spatial Structure of Simple Spiky Bursts at
Microwave/Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.;
Sakurai, T.; Grechnev, V. V.
Bibliographic Code: 2001ApJ...547.1090K
Abstract
We present the results of a study of spatial structure of sources of
microwave and millimeter bursts with simple spiky time profiles at 17
and 34 GHz, similar to those found to be common at 3 mm wavelength.
These bursts are of short duration, with fast 2-4 s rise time to peak,
followed by a rapid exponential decay. When mapped at high spatial
resolution with the Nobeyama Radio Heliograph (NoRH), the radio images
show direct evidence that the radio sources are compact bipolar loops:
source sizes are less than 5" and three of the five events studied show
closely spaced oppositely polarized components in the circular
polarization maps. All five events are located directly over magnetic
neutral lines in the photosphere. The soft X-ray behavior is not
entirely consistent with the Neupert effect in these events, since all
five events show a rise in the soft X-ray flux well before any
nonthermal electrons are present in the corona and the ratio of peak
soft X-ray flux to peak radio 17 GHz flux may vary by many orders of
magnitude from one event to the next. The abrupt time profiles of these
events and their physical properties are consistent with a single-loop
scenario in which magnetic energy release and acceleration of nonthermal
electrons are confined to a compact localized region.
@--------------------------------------------------------------------
Title: The Absolute Abundance of Iron in the Solar Corona
(CD-ROM Directory: contribs/white)
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.;
Kundu, M. R.
Bibliographic Code: 2001ASPC..223.1361W
Abstract
@--------------------------------------------------------------------
Title: Nonthermal Flare Emission from MEV-Energy Electrons
at 17, 34, and 86 GHZ
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.;
Sakurai, T.
Bibliographic Code: 2000ApJ...545.1084K
Abstract
We present analyses of two solar flares observed with high spatial
resolution at 86 GHz with the BIMA millimeter-wavelength telescope and
at 17 and 34 GHz with the Nobeyama radioheliograph. The flares were
observed on 1998 November 24 and 1999 May 1. At millimeter wavelengths
these are impulsive events, and therefore they must be produced by
MeV-energy electrons. The present study using simultaneous observations
of two flares at 86, 34, and 17 GHz provides an excellent opportunity to
study high-energy electrons with high spatial resolution observations at
three optically thin frequencies. The morphology of millimeter emission
can reveal both the properties of the MeV-energy electrons and the
nature of the coronal magnetic field lines where they radiate. One of
the two events we present is the first clear case of a lambda=3 mm
source in which both footpoints of a loop are detected. In the second
event the polarization image at 17 GHz also suggests a bipolar or
looplike morphology. Such morphological observations can be used to
constrain the nature of the magnetic field in the solar corona.
@--------------------------------------------------------------------
Title: Radio Detection of a Rapid Disturbance Launched by a
Solar Flare
Authors: Janardhan, P.; White, S. M.; Kundu, M. R.
Bibliographic Code: 2000SPD....31.0243J
Abstract
This paper reports 333 MHz observations of motion associated with a
solar flare at a speed of 26000 km s-1. The motion is seen
from a radio source which suddenly starts moving during the flare. At
its peak the radio source covers a quiet region of dimension 500 arcsec.
The disturbance itself does not seem to radiate, but it excites coronal
features which continue to radiate after it passes. The inferred
velocity is larger than any previously inferred velocity of a
disturbance in the solar atmosphere apart from freely-streaming beams of
accelerated electrons. The observed motion of the source at a fixed
frequency, low polarization and moderate bandwidth are more consistent
with the typical properties of moving Type IV radio bursts than with
classical coronal--shock--associated Type II bursts.
@--------------------------------------------------------------------
Title: Soft X-Ray and Gyroresonance Emission above Sunspots
Authors: Nindos, A.; Kundu, M. R.; White, S. M.;
Shibasaki, K.; Gopalswamy, N.
Bibliographic Code: 2000ApJS..130..485N
Abstract
Using Yohkoh SXT and Nobeyama 17 GHz data, we have studied the soft
X-ray and microwave emission above several stable, large sunspots near
central meridian passage. Our study confirms the well-known fact that
soft X-ray emission is depressed above sunspots. It also shows that the
distribution of their soft X-ray intensity is not uniform; usually the
darkest pixels are associated with the umbra or the far edges of the
leading part of the penumbra while the following part of the penumbra
may contain higher intensity pixels associated with brighter loops. For
the first time, we present a systematic survey of the temperatures and
emission measures of the soft X-ray material above sunspots. Sunspots
always contain the lowest temperatures and emission measures in the
active regions. The mean umbral temperature is 1.8×106
K, and the mean penumbral temperature is 2.4×106 K. The
mean umbral and penumbral emission measures are logEM=26.60
cm-5 and logEM=27.00 cm-5, respectively. The
differences between the umbral and penumbral plasma temperatures are
physically significant. The higher penumbral values imply that the loops
associated with the penumbrae are generally hotter and denser than the
loops associated with the umbrae. The highest sunspot temperatures and
emission measures are still lower than the average active region
parameters but higher than the quiet-Sun plasma parameters. The coronal
radiative energy loss rate above the umbrae is 15% higher than the
radiative loss rate of the quiet-Sun plasma but a factor of 8.3 lower
than the typical active region radiative loss rate. The radio emission
comes from the gyroresonance mechanism, and, as expected, it is
sensitive to the magnetic field rather than the soft X-ray-emitting
plasma.
@--------------------------------------------------------------------
Title: The Absolute Abundance of Iron in the Solar Corona
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.;
Kundu, M. R.
Bibliographic Code: 2000SPD....31.1301W
Abstract
We present a measurement of the abundance of Fe relative to H in the
solar corona using a technique which differs from previous spectroscopic
and solar wind measurements. Our method combines EUV line data from the
CDS spectrometer on SOHO with thermal bremsstrahlung radio data from the
VLA. The coronal Fe abundance is derived by equating the thermal
bremsstrahlung radio emission calculated from the EUV Fe line data to
that observed with the VLA, treating the Fe/H abundance as the sole
unknown. We apply this technique to a compact cool active region and
find Fe/H = 1.56 x 10-4, or about 4 times its value in the
solar photosphere. Uncertainties in the CDS radiometric calibration, the
VLA intensity measurements, the atomic parameters, and the assumptions
made in the spectral analysis yield net uncertainties of order 20%. This
result implies that low first ionization potential elements such as Fe
are enhanced in the solar corona relative to photospheric values.
@--------------------------------------------------------------------
Title: LASCO and EIT observations of CMEs associated with
flares
Authors: Zhang, J.; Dere, K. P.; Howard, R. A.; Kundu, M. R.;
White, S. M.
Bibliographic Code: 2000SPD....31.0906Z
Abstract
Coronal mass ejections (CME) and flares are two primary causes of
adverse space weather. These two solar eruptive phenomenon are often
observed to be associated with each other. Yet the relationship between
them is not well known. With unprecedented LASCO (Large-Angle and
Spectrometric Coronagraph) and EIT (Extreme-ultraviolet Imaging
Telescope) observations combined with simultaneous HXT (Hard X-ray
Telescope), GOES and other flare observations, we pursue to make a
comprehensive study on the spatial, temporal and energetic relationship
between CMEs and flares. In order to make accurate measurement of the
onset time of CMEs, we primarily select CME events whose source regions
are close to the limb and which are well observed by LASCO/C1 from 1.1
to 3 solar radii. Although a flare occurs in a rather small area of
active region, the CME's source region often covers much larger
longitudinal and latitudinal extension. Some CMEs occur simultaneously
with flare (within only a few minutes), however, some CMEs occur well
before the flares (more than 30 minutes earlier). Fast CMEs are
associated with strong flares. These studies are aimed to understand the
initiation process of solar eruptive phenomenon, and to fit a variety of
observational aspects into a consistent picture.
@--------------------------------------------------------------------
Title: Observations and Models of a Flaring Loop
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
Bibliographic Code: 2000SPD....31.0243N
Abstract
Simultaneous images of a flaring loop at two frequencies are used to
model the magnetic structure of the loop and the energy distribution of
the radiating electrons. The imaging data were obtained with the VLA at
5 and 15 GHz. Additional spectral data were provided by the OVRO Solar
Array at several frequencies between 2 GHz and 15 GHz. At 15 GHz, the
flare emission was optically thin and came from the footpoints of the
flaring loop, while at 5 GHz the loop itself was outlined. Most of the 5
GHz emission was optically thick and its spatial maximum was close to
the loop top. A striking feature of the observations is that the 5 GHz
emission does not reach down to the 15 GHz footpoints. We compare the
observations with calculations of gyrosynchrotron emission from an
inhomogeneous magnetic loop in order to determine the conditions in the
flaring loop. The best fit to the OVRO fluxes was reached with a model
flaring loop with photospheric footpoint magnetic field strength of 870
G. The thickness of the model loop was small compared to its footpoint
separation. The energy spectral index of the energetic electrons was 3.7
and their number density was 7.9 x 107 cm-3. The
low and high energy cutoffs of the nonthermal electrons were 8 and 210
keV. The 5 GHz emission in this model is at low harmonics (3--7) and
harmonic effects are responsible for the weak 5 GHz emission at the
footpoints. The absence of electrons above 210 keV is necessary in this
model to explain why no emission is observed from the loop top at 15
GHz. That model reproduced well the high frequency part of the OVRO flux
spectrum as well as the VLA spatial structure. Thus comparisons between
the spatially--resolved observations and models reveal the
three-dimensional structure of the loop geometry.
@--------------------------------------------------------------------
Title: Microwave/Millimeter Wavelength Bursts with Simple
Spiky Time Profiles
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.;
Sakurai, T.
Bibliographic Code: 2000SPD....31.0242K
Abstract
We report the detection at 17 and 34 GHz of microwave and millimeter
bursts which have simple spiky time profiles similar to those found to
be common at lambda = 3 mm. These bursts are of short duration, with
fast 2 - 4 sec rise time to peak, followed by an exponential decay.
These bursts can be of any intensity, from 1 sfu to 10's of sfu; they
are very strongly polarized (> 50%), and they have similar properties
regardless of the nature of the active region in which the bursts
originate. The bursts seem to originate in compact sources which are
generally unresolved with 15" and 7" resolution of the Nobeyama Radio
Heliograph at 17 and 34 GHz respectively. We provide both direct and
indirect evidence that these compact sources are low-lying bipolar
loops. The direct evidence follows from the physical appearance of the
loop as well as from the bipolar nature of the loop. The indirect
evidence follows from the offset in position of the footpoint emission
in microwaves and hard X-rays, implying a compact asymmetric loop with
microwaves originating from the stronger magnetic field foot point and
the hard X-rays originating from the weaker field foot point.
@--------------------------------------------------------------------
Title: Observations and models of a flaring loop.
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
Bibliographic Code: 2000BAAS...32..818N
Abstract
@--------------------------------------------------------------------
Title: The Absolute Abundance of Iron in the Solar Corona
Authors: White, S. M.; Thomas, R. J.; Brosius, J. W.;
Kundu, M. R.
Bibliographic Code: 2000ApJ...534L.203W, eprint = astro-ph/0004007
Abstract
We present a measurement of the abundance of Fe relative to H in the
solar corona using a technique that differs from previous spectroscopic
and solar wind measurements. Our method combines EUV line data from the
Coronal Diagnostic Spectrometer (CDS) on the Solar and Heliospheric
Observatory with thermal bremsstrahlung radio data from the VLA. The
coronal Fe abundance is derived by equating the thermal bremsstrahlung
radio emission calculated from the EUV Fe line data to that observed
with the VLA, treating the Fe/H abundance as the sole unknown. We apply
this technique to a compact cool active region and find
Fe/H=1.56×10-4, or about 4 times its value in the solar
photosphere. Uncertainties in the CDS radiometric calibration, the VLA
intensity measurements, the atomic parameters, and the assumptions made
in the spectral analysis yield net uncertainties of ~20%. This result
implies that low first ionization potential elements such as Fe are
enhanced in the solar corona relative to photospheric values.
@--------------------------------------------------------------------
Title: Radio Detection of a Rapid Disturbance Launched by a
Solar Flare
Authors: White, S. M.; Janardhan, P.; Kundu, M. R.
Bibliographic Code: 2000ApJ...533L.167W
Abstract
We report the direct observation of motion associated with a solar flare
at a speed of 26,000 km s-1. The motion is seen from a radio
source at 0.33 GHz, which suddenly starts moving during the flare. At
its peak, the radio source covers a quiet region of dimension 500".
Emission from any given location is sporadic. The disturbance itself
does not seem to radiate, but it excites coronal features that continue
to radiate after it passes. The inferred velocity is larger than any
previously inferred velocity of a disturbance in the solar atmosphere
apart from freely streaming beams of accelerated electrons. The observed
motion of the source at a fixed frequency, low polarization, and
moderate bandwidth are more consistent with the typical properties of
moving type IV radio bursts than with classical coronal shock-associated
type II bursts, but any disturbance at such a high velocity must be
highly supersonic and should drive a shock. We speculate that the
disturbance is associated with the realignment of magnetic fields
connecting different portions of an active region.
@--------------------------------------------------------------------
Title: Observations and Models of a Flaring Loop
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
Bibliographic Code: 2000ApJ...533.1053N
Abstract
Simultaneous images of a flaring loop at two frequencies are used to
model the magnetic structure of the loop and the energy distribution of
the radiating electrons. The imaging data were obtained with the VLA at
5 and 15 GHz. Additional spectral data were provided by the Owens Valley
Radio Observatory (OVRO) solar array at several frequencies between 2
and 15 GHz. At 15 GHz, the flare emission was optically thin and came
from the footpoints of the flaring loop, while at 5 GHz the loop itself
was outlined. Most of the 5 GHz emission was optically thick, and its
spatial maximum was close to the loop top. A striking feature of the
observations is that the 5 GHz emission does not reach down to the 15
GHz footpoints. We compare the observations with calculations of
gyrosynchrotron emission from an inhomogeneous magnetic loop in order to
determine the conditions in the flaring loop. The best fit to the OVRO
fluxes was reached with a model flaring loop with photospheric footpoint
magnetic field strength of 870 G. The thickness of the model loop was
small compared with its footpoint separation. The energy spectral index
of the energetic electrons was 3.7, and their number density was
7.9×107 cm-3. The low- and high-energy
cutoffs of the nonthermal electrons were 8 and 210 keV, respectively.
The 5 GHz emission in this model is at low harmonics (3-7), and harmonic
effects are responsible for the weak 5 GHz emission at the footpoints.
The absence of electrons above 210 keV is necessary in this model to
explain why no emission is observed from the loop top at 15 GHz. That
model reproduced well the high-frequency part of the OVRO flux spectrum
as well as the VLA spatial structure. Thus, comparisons between the
spatially resolved observations and models reveal the three-dimensional
structure of the loop geometry.
@--------------------------------------------------------------------
Title: Observations and Models of a Flaring Loop
Authors: Nindos, A.; White, S. M.; Kundu, M. R.; Gary, D. E.
Bibliographic Code: 2000ASPC..206..359N
Abstract
@--------------------------------------------------------------------
Title: Millimeter-Interferometer Observations of Flares in
Conjunction with HESSI
Authors: White, S. M.; Kundu, M. R.
Bibliographic Code: 2000ASPC..206..335W
Abstract
@--------------------------------------------------------------------
Title: Nonthermal Flare Emission from MeV-Energy Electrons
at 17, 34, and 86, GHz
Authors: Kundu, M. R.; White, S. M.; Shibasaki, K.;
Sakurai, T.
Bibliographic Code: 2000ASPC..206..307K
Abstract
@--------------------------------------------------------------------
Title: A Microwave Study of Coronal and Chromospheric
Ejecta
Authors: Nindos, A.; Kundu, M. R.; Raulin, J.-P.;
Shibasaki, K.; White, S. M.; Nitta, N.; Shibata, K.;
Shimojo, M.
Bibliographic Code: 1999spro.proc..135N
Abstract
We have studied the radio properties of 18 X-ray coronal jets (observed
by the Yohkoh SXT) using Nobeyama 17 GHz data. We also searched for
chromospheric ejecta (Halpha surges) during the time intervals that
the X-ray images were available. Microwave emission was associated with
the majority of the X-ray jets. The radio emission came from the base or
the lower part of the jets. We detected radio emission from almost all
jets which showed flare-like activity at their footpoints. The 17 GHz
time profiles were gradual and unpolarized, implying that the emission
was thermal. When possible, we computed the physical properties of the
X-ray-emitting ejected plasma. In one two-sided-loop type jet and one
anemone-type jet, the observed microwave fluxes from the lower part of
the jets were well above the fluxes predicted from the computed electron
temperatures and emission measures of the soft X-ray-emitting material
on the basis of thermal free-free emission. We interpreted the large
discrepancies in terms of the presence of lower temperature material
which cannot be detected by the SXT but produces strong microwave
free-free emission. This is the first time that such material is
observed in two-sided-loop type jets. Thus our observations confirm the
theoretical prediction by Yokoyama and Shibata (1996). We detected no
cool material at the base of the jets. We also observed an Halpha
surge which was not associated with an X-ray jet and showed no
signatures on the SXT images but was detected with the Nobeyama
Radioheliograph. The emission of the microwave surge-associated source
was free-free from the chromospheric plasma. Constraints for the surge
density were derived.
@--------------------------------------------------------------------
Title: Radio Observations of Weak Coronal Transients
Authors: Kundu, M. R.
Bibliographic Code: 1999spro.proc..111K
Abstract
In this review we discuss radio observations of weak coronal transients.
We concentrate on the transient events observed primarily by Yohkoh/SXT
and to a smaller extent by SOHO/EIT. The radio observations are those
obtained with the Very Large Array (VLA) in microwaves, the Nancay
(France) metric radioheliograph at 150 - 450 MHz and the Nobeyama
RadioHeliograph (NRH) at 17 GHz. We discuss the observational
characteristics of X-ray bright point flares at meter wavelengths and in
microwaves, and provide evidence that both thermal and nonthermal
processes occur in these small scale flaring events. Similarly, radio
observations of X-ray jets in microwaves and at meter wavelengths
provide evidence for both thermal and nonthermal processes in these
dynamic coronal phenomena. Nonthermal radio emission in the form of
metric type III bursts is produced by electron beams propagating along
the jet, whereas microwave emission comes mostly from the jet base. We
discuss active region transient brightenings (ARTB's) and show that
their radio emission can be purely thermal, thermal gyro- resonance or
nonthermal gyrosynchrotron radiation. We discuss one form
(radio-selected) of quiet Sun transient brightenings located far from
active regions. We provide evidence that weak plasma ejections following
flares is observed at metric wavelengths in the form of transient
continuum emission. Finally, we discuss the time-varying polar
brightenings at 17 GHz, and their relationship to polar erupting plumes
observed by SOHO-EIT.
@--------------------------------------------------------------------
Title: Active Region Emissions and Coronal Field
Extrapolations
Authors: Lee, J.; White, S. M.; Kundu, M. R.; Mikic, Z.
Bibliographic Code: 1999spro.proc...65L
Abstract
With vector magnetographs set to fly on the Solar--B mission, the
extrapolation of photospheric magnetic fields into the corona will be
increasingly important. As the techniques of coronal field
extrapolations grow more sophisticated, we require a more powerful means
to test them and to make full use of the information they contain. Radio
data can play an important role in testing extrapolation methods. In
this paper, we discuss a new test of coronal field extrapolation using
the concept of field line connectivity. The motivating idea is that
temperature should be nearly uniform on a given magnetic field line due
to the rapid transport of physical quantities along field lines in the
corona. Optically--thick gyroresonance emission provides the temperature
on a surface of known magnetic field strength in the corona. As a
consequence, we may expect that radio intensities observed at different
frequencies at points connected by field lines should show a good
correlation. This suggests that a test of a magnetic field extrapolation
model is whether the field--line connectivity it predicts shows such a
correlation. A second application of field--line connectivity is to try
to understand the relationship between physical quantities in the
photosphere at the footpoints of magnetic field lines and the heating
process in the corona on the same field lines. If a particular magnetic
quantity, such as shear, plays a role in coronal heating then one
expects the coronal extension of field lines passing through peaks in
this quantity will show the highest coronal temperatures. This idea can
be used to test candidate coronal heating mechanisms. We demonstrate
these ideas using the combination of high--resolution VLA observations
of a complex active region together with state--of--the--art nonlinear
force--free field modeling.
@--------------------------------------------------------------------
Title: Two-Temperature Coronal Models from SOHO/EIT
Observations
Authors: Zhang, J.; White, S. M.; Kundu, M. R.
Bibliographic Code: 1999ApJ...527..977Z
Abstract
We present a method for deriving a two-thermal-component approximation
to the differential emission measure distribution of plasma in the Sun's
corona in the temperature range to which the Extreme-Ultraviolet Imaging
Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO)
spacecraft is sensitive. EIT takes high-resolution full-disk coronal
images in three of its four optimized channels by observing emission
lines of highly ionized Fe whose formation temperatures overlap and
cover the range from 0.7 to 2.8 MK. It is straightforward to show that
the traditional single-temperature models based on the ratio of a pair
of EIT images at different wavelengths are not able adequately to
represent the plasma contributing to all three wavelength ranges. In
this paper, we develop a modified image-ratio method that results in a
two-thermal-component model for the plasma producing the coronal
emission observed by EIT. The products of this method are two
temperature and two emission measure full-disk maps of the Sun's corona,
with the full resolution of the EIT telescope, in two temperature
regimes: one from 0.8 to 1.6 MK and the other from 1.6 to 2.6 MK. The
two-component solutions are tested using a series of model differential
emission measures (DEMs) from the CHIANTI atomic database package. This
method appears to produce realistic results in all regions of the Sun's
atmosphere with the exception of coronal holes, where very cool Si
VII/Mg VII lines (<0.7 MK) contribute more to the EIT 284 Å
image than the otherwise dominant hot Fe XV lines and result in
unrealistically high temperatures for the hot component there. We
demonstrate that while the raw EIT images are dominated by the spatial
distribution of emission measure in the corona, the temperature maps
often emphasize fine structure, which is less visible in the flux
images. The emission measure of the hot component is always larger than
that of the cool component. On the disk there appears to be a firm lower
limit to the integrated column emission measure along any line of sight,
including toward coronal holes. There is no overall correlation between
temperature and emission measure.
@--------------------------------------------------------------------
Title: Microwave and Extreme Ultraviolet Observations of
Solar Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
Bibliographic Code: 1999ApJ...527..415N
Abstract
The poles of the Sun are brighter than the rest of the quiet Sun's
emission in a limited range of radio frequencies from 17 GHz to 87 GHz.
We have studied microwave images of the quiet Sun made with the Nobeyama
radioheliograph at 17 GHz. They show that the so-called polar-cap
brightening consists of two components: a diffuse component of 1500 K
excess brightness and patchy compact sources with localized excess
brightness of about 3500 K. We test the reality of the compact sources
using the maximum entropy method deconvolution. The total flux and the
number of compact polar sources as well as the north-south extent of the
diffuse polar emission are larger in the pole that is closest to the
Earth. We compared the microwave polar emission with nearly simultaneous
SOHO EIT images taken in the lines of He II at 304 Å and Fe XII at
195 Å. No one-to-one correlation between the compact radio sources
and the bright EUV features was found: most of the radio emission arises
between the plumes visible to EIT. The boundaries of the polar-cap
brightenings did not match exactly the boundaries of the coronal holes
as seen in either the Fe XII 195 Å images or the He II 304 Å
images. The temporal variations of the compact microwave sources did not
correspond to any significant changes in EUV emission. On the other
hand, most He II 304 Å changing features were associated with the
diffuse polar microwave emission, which was practically constant. Our
data suggest that the origin of the polar brightening is not coronal; it
seems that the bulk of the patchy radio emission comes from heights
below the 80,000 K layer.
@--------------------------------------------------------------------
Title: Radio and X-Ray Imaging Observations of a Continuum
Burst
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.; Raoult, A.
Bibliographic Code: 1999ApJ...522.1100K
Abstract
We study a metric continuum burst observed on 1993 February 18, and its
X-ray signatures from imaging observations in radio and X-rays using the
Nançay radioheliograph and the Yohkoh Soft X-Ray Telescope (SXT).
The event in question was associated with weak type III bursts; these
were detected at only one frequency (164 MHz), except for one burst (at
10:58:05 UT), which was observed over a broad frequency range (164-435
MHz). We believe that the early metric continuum burst is an extension
of the microwave continuum which was observed at frequencies as high as
5 GHz, and its onset at ~10:50 UT is associated with the development of
an X-ray-emitting diffuse loop system which appears to advance with a
speed of ~50-100 km s^-1. The observed type III bursts seem to
correspond to the repeated occurrence/appearance of a collimated jet
emanating from the loop system that is responsible for the continuum
burst. A few minutes prior to the main continuum onset there is a soft
X-ray ejection from the main flare region. The main continuum has a
brightness temperature greater than 10^8 K; it is unpolarized, and it
shows dispersion in position with frequency and moves with speeds of ~50
km s^-1 at 236-410 MHz. The SXT images reveal that this initially
ejected soft X-ray-emitting hot plasma seems to gradually fill up the
loop system with hot material. This hot plasma must contain enough
energetic electrons of energy greater than several tens of keV, which
are responsible for producing the metric continuum burst by plasma
radiation mechanism.
@--------------------------------------------------------------------
Title: Multiple Components in the Millimeter Emission of a
Solar Flare
Authors: Raulin, J.-P.; White, S. M.; Kundu, M. R.;
Silva, A. V. R.; Shibasaki, K.
Bibliographic Code: 1999ApJ...522..547R
Abstract
We analyze a small flare using imaging data at millimeter, microwave,
and soft X-ray wavelengths and microwave and hard X-ray spectral
observations. The remarkable aspect of this flare is evidence for the
presence of MeV-energy electrons, which are responsible for the
nonthermal millimeter emission, at a time when no hard X-rays from lower
energy electrons are detected. This occurs during a smoothly varying
phase, which is seen at radio wavelengths to last several minutes and is
the brightest phase at millimeter wavelengths but is undetected in hard
X-rays: it follows a brief spike of emission at flare onset, which has
the more usual properties of impulsive events and features nonthermal
microwave, millimeter, and hard X-ray emission. We interpretthe phase
that is brightest at millimeter wavelengths as being due to efficient
trapping of a relatively small number of nonthermal electrons, whereas
during the hard X-ray emission, trapping is much less efficient, and the
decay time is much shorter at all energies, which leads to a larger
ratio of hard X-ray flux to radio flux. As in many previous events
studied at millimeter wavelengths, there is a discrepancy between the
electron energy spectral indices inferred from the milllimeter and hard
X-ray data during the impulsive phase when both are detected: again it
appears that the energy spectrum at 1 MeV must be significantly flatter
than at several hundred keV and below. However, there are problems in
reconciling quantitatively the energy spectra for the hard
X-ray-emitting and radio-emitting components: based on the most
plausible parameters, the radio-emitting electrons should produce most
of the hard X-rays. One solution to this contradiction is to invoke a
coronal magnetic field stronger than seems likely based on the
photospheric magnetic field.
@--------------------------------------------------------------------
Title: A Microwave Study of Coronal Ejecta
Authors: Kundu, M. R.; Nindos, A.; Raulin, J.-P.;
Shibasaki, K.; White, S. M.; Nitta, N.; Shibata, K.;
Shimojo, M.
Bibliographic Code: 1999ApJ...520..391K
Abstract
Using Nobeyama 17 GHz data, we have studied the radio properties of 19
coronal jets identified in Yohkoh soft X-ray imaging telescope (SXT)
X-ray observations. The radio data provide information on the physical
conditions in the jets, which complements the data from the X-ray
surveys. Microwave emission was associated with the majority of the
X-ray jets in our sample. The radio emission typically came from the
base or the base and lower part of the jets. We detected radio emission
from almost all jets that showed flarelike activity at their bases. The
jets that were not associated with radio emission did not show any
significant increase in X-ray emission at their bases. The strongest
radio emission came from two of the largest jets in our sample. Our data
show a general correlation between the X-ray jet fluxes and the
associated radio fluxes. The 17 GHz time profiles were gradual and
unpolarized, implying that the emission was thermal. In a two-sided-loop
jet (1992 July 22 event) and one anemone-type jet (1993 February 9
event), the observed microwave fluxes from the lower part of the jets
were well above the fluxes calculated from the computed physical
parameters of the soft X-ray-emitting material on the basis of thermal
free-free emission. We interpret the large discrepancies in terms of the
presence of lower temperature material, which cannot be detected by the
SXT (the SXT is most sensitive to hot plasma above 2x10^6 K), but which
produces strong microwave free-free emission. This is the first time
that such material has been observed in two-sided-loop-type jets. We
also observed motion of a jet-associated microwave source with a
velocity of 55 km s^-1. The microwave motion occurred after the
appearance of the X-ray jet. There is clear evidence that the microwave
emission of that source was associated with the jet and not with the
associated small flare.
@--------------------------------------------------------------------
Title: Millimeter Imaging Observations of High Energy
Electrons in Solar Flares
Authors: White, S. M.; Kundu, M. R.
Bibliographic Code: 1999AAS...194.8009W
Abstract
The 10-element BIMA array will be used in to image solar flares at
millimeter wavelengths during campaign periods in the upcoming solar
maximum. Since millimeter emission in the impulsive phase of flares
comes from electrons with energies typically in excess of 1 MeV, these
observations complement observations of lower energy electrons at other
wavelengths. Recent BIMA flare data will be presented and plans for the
near future will be discussed.
@--------------------------------------------------------------------
Title: Microwave and Extreme Ultraviolet Observations of
Solar Polar Regions
Authors: Nindos, A.; Kundu, M. R.; White, S. M.; Gary, D. E.;
Shibasaki, K.; Dere, K. P.
Bibliographic Code: 1999AAS...194.3207N
Abstract
The radio emission of solar poles is brighter than the rest of the quiet
Sun's emission in a limited range of frequencies from 17 GHz to 87 GHz.
We have studied microwave images of the quiet Sun made with the Nobeyama
Radioheliograph at 17 GHz. They show that the so-called polar-cap
brightening consists of two components: a diffuse component of 1500 K
excess brightness, and patchy compact sources with localized excess
brightness of about 3500 K. The total flux and the number of compact
polar sources as well as the North-South extent of the diffuse polar
emission are larger in the pole which is closest to the Earth. We
compared the microwave polar emission with nearly simultaneous SoHO EIT
images taken in the lines of He ii at 304 Angstroms and Fe xii at 195
Angstroms. No one-to-one correlation between the compact radio sources
and the bright EUV features was found: most of the radio emission arises
between the plumes visible to EIT. The boundaries of the polar-cap
brightenings did not match exactly the boundaries of the coronal holes
as seen in the Fe xii 195 Angstroms images. The temporal variations of
the compact microwave sources did not correspond to any significant
changes in EUV emission. On the other hand, most He ii 304 Angstroms
changing features were associated with the diffuse polar microwave
emission which was practically constant. Our data suggest that the
origin of the polar brightening is not coronal; it seems that the bulk
of the patchy radio emission comes from heights below the 80000 K layer.
@--------------------------------------------------------------------
Title: A Microwave Study of Coronal Ejecta
Authors: Kundu, M. R.; Nindos, A.; Raulin, J.-P.;
Shibasaki, K.; White, S. M.; Nitta, N.; Shibata, K.;
Shimojo, M.
Bibliographic Code: 1999AAS...194.1704K
Abstract
Using Nobeyama 17 GHz data, we have studied the radio properties of 19
coronal jets identified in Yohkoh SXT X-ray observations. The radio data
provide information on the physical conditions in the jets which
complements the data from the X-ray surveys. Microwave emission was
associated with the majority of the X-ray jets in our sample. The radio
emission typically came from the base or the base and lower part of the
jets. We detected radio emission from almost all jets which showed
flare-like activity at their bases. The jets which were not associated
with radio emission did not show any significant increase in X-ray
emission at their bases. The strongest radio emission came from two of
the largest jets in our sample. Our data show a general correlation
between the X-ray jet fluxes and the associated radio fluxes. The 17 GHz
time profiles were gradual and unpolarized, implying that the emission
was thermal. In a two-sided-loop jet (July 22, 1992 event) and one
anemone-type jet (February 9, 1993 event), the observed microwave fluxes
from the lower part of the jets were well above the fluxes calculated
from the computed physical parameters of the soft X-ray-emitting
material on the basis of thermal free-free emission. We interpret the
large discrepancies in terms of the presence of lower temperature
material which cannot be detected by the SXT (the SXT is most sensitive
to hot plasma above 2 x 10(6) K) but which produces strong microwave
free-free emission. This is the first time that such material has been
observed in two-sided-loop type jets. We also observed motion of a
jet-associated microwave source with a velocity of 55 km/sec. The
microwave motion occurred after the appearance of the X-ray jet. There
is clear evidence that the microwave emission of that source was
associated with the jet and not with the associated small flare.
@--------------------------------------------------------------------
Title: The Sun's Corona viewed from EUV and Radio
Wavelengths
Authors: Zhang, J.; Kundu, M. R.; White, S. W.
Bibliographic Code: 1999AAS...194.1608Z
Abstract
The Sun's Corona, which is composed of a few million degree plasma, can
be best viewed in two electro-magnetic wavelength domains, one from a
few Angstrom to hundreds of Angstrom (in Soft X-ray and EUV domains),
the other from a few centimeter to several tens of centimeter
wavelengths (in radio domain). In this paper, we present the detailed
and quantitative comparison of corona observations made in these two
domains with high spatial resolution and full view of the Sun. The EUV
observations were taken with EIT (Extreme Ultraviolet Imager) on board
SOHO (Solar and Heliospheric Observatory) in Fe spectral lines centered
at 171, 195 and 284 Angstrom, respectively; while the radio observations
were taken with the VLA (Very Large Array) at 6 and 20 cm, and NRH
(Nobeyama Radio Heliograph) at 1.8 cm (17 Ghz), respectively. We have
found that there exists excellent morphological similarity of corona
features between these two sets of observations. However, the
quantitative comparisons have revealed that the predicted radio flux
from EUV observations based on traditional assumptions is always higher
than that observed directly by radio instruments, by a factor of 4 to 6.
The discrepancy is probably due to the underestimation of coronal ion
abundance (e.g. Meyer's abundance) by a factor of 4 to 6.
@--------------------------------------------------------------------
Title: A Study of Microwave-selected Coronal Transient
Brightenings
Authors: Nindos, A.; Kundu, M. R.; White, S. M.
Bibliographic Code: 1999ApJ...513..983N
Abstract
We present the results of a search for radio-selected transient
brightenings (TBs) in the solar atmosphere as a complement to the more
common X-ray-selected surveys. The Sun was generally quiet during the
observations, making these data sensitive to weak TBs both in and
outside active regions. Five small impulsive events were identified in a
set of VLA observations at 4.5, 1.5, and 0.33 GHz and compared with soft
X-ray images from Yohkoh and EUV images from SOHO/EIT. Four of the
events were located at the edges of an active region, but one was
located 100" away in a quiet region of the atmosphere. Possible emission
mechanisms for these brightenings are investigated. The time profiles of
the radio TBs show impulsive peaks, while the corresponding soft X-ray
profiles are gradual. The impulsive radio peaks were up to 35%
polarized. Our data favor an interpretation in terms of gyrosynchrotron
radiation from mildly relativistic electrons. A small number of
nonthermal electrons with spectral index 3 can explain the observed
properties of the TBs. Thus, nonthermal TBs can be found away from
active regions. Two of the microwave TBs also show evidence for type III
radio emission at 327 MHz.
@--------------------------------------------------------------------
Title: University of Maryland, Department of Astronomy,
College Park, Maryland 20742. Report for the period
1 Oct 1997 - 30 Sep 1998.
Authors: Kundu, M. R.
Bibliographic Code: 1999BAAS...31..194K
Abstract
@--------------------------------------------------------------------
Title: The Height Structure of the Solar Atmosphere from
the Extreme-Ultraviolet Perspective
Authors: Zhang, Jie; White, S. M.; Kundu, M. R.
Bibliographic Code: 1998ApJ...504L.127Z, eprint = astro-ph/9807175
Abstract
We investigate the structure of the solar chromosphere and transition
region using full Sun images obtained with the Extreme-Ultraviolet
Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory
spacecraft. The limb seen in the EIT coronal images (taken in lines of
Fe IX/X at 171 A, Fe XII at 195 A, and Fe XV at 284 A) is an absorption
limb predicted by models to occur at the top of the chromosphere where
the density of neutral hydrogen becomes significant (~1010 cm-3). The
transition-region limb seen in He II lambda 304 images is an emission
limb. We find that (1) the limb is higher at the poles than at the
equator both in the coronal images (by 1300+/-650 km) and the 304 A
images (by 3500+/-1200 km), and (2) the 304 A limb is significantly
higher than the limb in the coronal images. The height difference is
3100+/-1200 km at the equator and 6600+/-1200 km at the poles. We
suggest that the elevation of the 304 A limb above the limb in the
coronal images may be due to the upper surface of the chromosphere being
bumpy, possibly because of the presence of spicules. The polar extension
is consistent with a reduced heat input to the chromosphere in the polar
coronal holes compared with the quiet-Sun atmosphere at the equator.
@--------------------------------------------------------------------
Title: Spatial Structure of Solar Coronal Magnetic Loops
Revealed by Transient Microwave Brightenings
Authors: Zhang, J.; Gopalswamy, N.; Kundu, M. R.;
Schmahl, E. J.; Lemen, J. R.
Bibliographic Code: 1998SoPh..180..285Z
Abstract
@--------------------------------------------------------------------
Title: Microwave Mode Coupling Above Active Regions as a
Coronal Density Diagnostic
Authors: Lee, Jeongwoo; White, Stephen M.; Kundu, M. R.;
Mikic, Zoran; McClymont, A. N.
Bibliographic Code: 1998SoPh..180..193L
Abstract
@--------------------------------------------------------------------
Title: University of Maryland, Department of Astronomy,
College Park, Maryland 20742. Report for the period
1 Oct 1996 - 30 Sep 1997.
Authors: Kundu, M. R.
Bibliographic Code: 1998BAAS...30..233K
Abstract
@--------------------------------------------------------------------
Title: Microwave and Soft X-ray Study of Solar Active
Region Evolution
Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.;
Perez-Enriquez, R.; Koshiishi, H.; Enome, S.
Bibliographic Code: 1998SoPh..178..353L
Abstract
@--------------------------------------------------------------------
Title: Two-Sided-Loop Type X-ray Jets and Metric Radio
Bursts
Authors: Kundu, M. R.; Raulin, J.-P.; Nitta, N.; Shibata, K.;
Shimojo, M.
Bibliographic Code: 1998SoPh..178..173K
Abstract
@--------------------------------------------------------------------
Title: The Solar Atmosphere Above a Sunspot
Authors: Zlotnik, E. Ya.; White, S. M.; Kundu, M. R.
Bibliographic Code: 1998ASPC..155..135Z
Abstract
@--------------------------------------------------------------------
Title: The Emergence of a Solar Active Region
Authors: White, S. M.; Lee, J.; Kundu, M. R.; SOHO/MDI Team
Bibliographic Code: 1998ASPC..155..130W
Abstract
@--------------------------------------------------------------------
Title: A Search for Hard X-ray Emission from Active Stars
Using CGRO/BATSE
Authors: White, S. M.; Harmon, B. A.; Lim, J.; Kundu, M. R.
Bibliographic Code: 1998ASPC..154.1192W
Abstract
We report the results of a search for > 20 keV photons from active
stars using CGRO/BATSE Earth-occultation observations. Twelve of the
"usual suspects" together with 12 "placebo" locations have been analyzed
using the BATSE software for occultation analysis developed at
NASA/MSFC. There are four detections at the nominal 5sigma level, and
eight at the 3sigma level. However the strongest detection (that of AB
Dor) shows clear evidence for contamination from the nearby strong
source LMC X-4. 18 of the 24 fields yield positive fluxes, indicating a
clear bias in the results, and possibly indicating the presence of weak
background hard X-ray sources detectable by BATSE in long-term studies.
@--------------------------------------------------------------------
Title: Synoptic Radio Observations
Authors: Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1998ASPC..140..387S
Abstract
@--------------------------------------------------------------------
Title: Detection of Microwave Emission from Coronal X-Ray
Jets
Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N.
Bibliographic Code: 1997ApJ...491L.121K
Abstract
We present evidence of the detection of microwave emission at 17 GHz in
association with coronal X-ray jets. We present two typical cases--one
on the disk (1995 March 31) and the other at the limb (1992 August 25).
For the disk event we see 17 GHz emission from the upper part of the jet
base (active region loop or loops), but no emission from the collimated
X-ray jet itself, implying that it must be optically thin at 17 GHz. For
the limb event, we see the base of the jet as well as the bottom part of
the jet itself, implying that the optical depth is higher at the bottom
part (obviously because of higher electron density) than at the top. We
believe that the 17 GHz emission is thermal, because it is gradual and
unpolarized, and that the heating process that gives rise to the jet
X-ray plasma also results in the 17 GHz emission. The calculated 17 GHz
flux densities seem to agree with the observed values within a factor of
2. We consider this disagreement to be quite reasonable in view of the
various uncertainties involved in computing the emission in both radio
and X-rays.
@--------------------------------------------------------------------
Title: Fast Time Structure during Transient Microwave
Brightenings: Evidence for Nonthermal Processes
Authors: Gopalswamy, N.; Zhang, J.; Kundu, M. R.;
Schmahl, E. J.; Lemen, J. R.
Bibliographic Code: 1997ApJ...491L.115G, eprint = astro-ph/9710200
Abstract
Transient microwave brightenings (TMBs) are small-scale energy releases
from the periphery of sunspot umbrae with a flux density 2 orders of
magnitude smaller than that from a typical flare. Gopalswamy et al.
first reported the detection of the TMBs, and it was pointed out that
the radio emission implied a region of very high magnetic field so that
the emission mechanism has to be gyroresonance or nonthermal
gyrosynchrotron, but not free-free emission. It was not possible to
decide between gyroresonance and gyrosynchrotron processes because of
the low time resolution (30 s) used in the data analysis. We have since
performed a detailed analysis of the Very Large Array data with full
time resolution (3.3 s) at two wavelengths (2 and 3.6 cm), and we can
now adequately address the question of the emission mechanism of the
TMBs. We find that nonthermal processes indeed take place during the
TMBs. We present evidence for nonthermal emission in the form of
temporal and spatial structure of the TMBs. The fast time structure
cannot be explained by a thermodynamic cooling time and therefore
requires a nonthermal process. Using the physical parameters obtained
from X-ray and radio observations, we determine the magnetic field
parameters of the loop and estimate the energy released during the TMBs.
The impulsive components of TMBs imply an energy release rate of ~
1.3x1022 ergs s ^{-1} , so the thermal energy content of the
TMBs could be less than ~ 1024 ergs.
@--------------------------------------------------------------------
Title: X-Ray and Radio Studies of a Coronal Eruption: Shock
Wave, Plasmoid, and Coronal Mass Ejection
Authors: Gopalswamy, N.; Kundu, M. R.; Manoharan, P. K.;
Raoult, A.; Nitta, N.; Zarka, P.
Bibliographic Code: 1997ApJ...486.1036G
Abstract
On 1994 July 31, a fast (900 km s-1) eruptive structure was observed in
X-rays, followed by a slower plasmoid (180 km s-1). They were associated
with a coronal mass ejection, prominence eruption, and a host of metric
radio bursts. The X-ray structure seems to be a part of a white light
coronal mass ejections (CME), as inferred from the white light images of
July 30 and 31. A type II burst was observed at the leading edge of the
X-ray eruption, while a type IV burst was spatially associated with the
detached plasmoid. The type III radio bursts occurred on thin overdense
structures associated with the eruption. We detected the rise of plasma
levels because of mass addition to the type III burst sources as a
result of the eruption. This event further clarifies the manifestation
of a CME in X-rays. We identify the X-ray eruption as the driver of the
coronal shock wave. This provides answer to the long-standing question
regarding the origin of coronal and interplanetary shock waves. We have
also found evidence to support the idea that herringbone bursts are
produced when the coronal shock wave crosses open magnetic field lines.
@--------------------------------------------------------------------
Title: Signatures of Coronal Currents in Microwave Images
Authors: Lee, Jeongwoo; White, Stephen M.; Gopalswamy, N.;
Kundu, M. R.
Bibliographic Code: 1997SoPh..174..175L
Abstract
@--------------------------------------------------------------------
Title: Radio Observations of Gyroresonance Emission from
Coronal Magnetic Fields
Authors: White, S. M.; Kundu, M. R.
Bibliographic Code: 1997SoPh..174...31W
Abstract
@--------------------------------------------------------------------
Title: Currents, Magnetic Fields and Heating in a Solar
Active Region
Authors: Lee, J.; McClymont, A. N.; Mikic, Z.; White, S. M.;
Kundu, M. R.
Bibliographic Code: 1997SPD....28.1602L
Abstract
We have compared high-quality microwave images of the radio emission
from the corona above an active region with state-of-the-art nonlinear
force-free extrapolations of the photospheric magnetic field. The radio
images, which are dominated by the opacity provided by the coronal
magnetic fields, show excess magnetic field in locations consistent with
the expected location of coronal currents. We test the hypothesis that
the degree of heating on a given coronal magnetic flux tube is related
to the current flowing through it by comparing model radio brightness
distributions at different frequencies with the actual observations. In
the model we assume that temperature is distributed along the field
lines according to quasi-static loop models, and that there is
effectively no diffusion across the field lines. This coronal heating
model is able to reproduce the radio brightness distributions remarkably
well.
@--------------------------------------------------------------------
Title: Radio Observations of the Emergence of a Solar
Active Region
Authors: White, S. M.; Lee, J.; Kundu, M. R.
Bibliographic Code: 1997SPD....28.0603W
Abstract
On July 6 1996 a solar active region abruptly began to emerge through
the solar photosphere. This region was eventually to produce the first
X-class flare since 1993. We happened to be observing the region with
the VLA during its emergence, and present a preliminary report on the
observations in this paper. The radio data are the only means for
observing the magnetic fields of the emerging region in the corona, and
can thus be used to test models for the structure of emerging magnetic
fields. In this case, we do not see any evidence for strong coronal
fields during the initial emergence, indicating that the field lines
diverge rapidly above the photosphere as expected from simple theory. We
follow the emergence of flux over several days and discuss the
implications of these observations for theories of flux emergence.
@--------------------------------------------------------------------
Title: Tracking a CME from Cradle to Grave: A
Multi-wavelength Analysis of the February 6-7, 1997
Event
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.;
Kosugi, T.; Hudson, H.; Nitta, N.; Thompson, B.;
Gurman, J.; Plunkett, S.; Howard, R.; Burkepile, J.
Bibliographic Code: 1997SPD....28.0501G
Abstract
The partially earth-directed coronal mass ejection (CME) event of 1997
February 6-7 originated from the southwest quadrant of the sun. The CME
accelerated from 170 km/s to about 830 km/s when it reached a distance
of 25 solar radii. The CME was an arcade eruption followed by bright
prominence core structures. The prominence core was tracked continuously
from the solar surface to the interplanetary medium by combining data
from the Nobeyama radioheliograph (microwaves), Mauna Loa Solar
Observatory (He 10830 { Angstroms}), SOHO/EIT (EUV) and SOHO/LASCO
(white light). The CME was accompanied by an arcade formation, fully
observed by the YOHKOH/SXT (soft X-rays) and SOHO/EIT (EUV). The X-ray
and EUV observations suggest that the reconnection proceeded from the
northwest end to the southeast end of a filament channel. In the
SOHO/EIT images, the the feet of the soft X-ray arcade were observed as
EUV ribbons. The CME event also caused a medium sized geomagnetic storm:
The hourly equatorial Dst values attained storm level during 18:00-19:00
UT on February 09. This means the disturbance took about 2.25 days to
reach the Earth. The first signatures of an IP shock was a pressure jump
in the WIND data around 13:00 UT on Feb 09, 1997 which lasted for about
14 hours, followed by flux rope signatures. This CME event confirms a
number of ideas about CMEs: The three part structure (frontal bright
arcade, dark cavity and prominence core), disappearing filament,
elongated arcade formation, and terrestrial effects. We make use of the
excellent data coverage from the solar surface to the Earth to address a
number of issues regarding the origin and propagation of the
geoeffective solar disturbances. We benefited from discussions at the
first SOHO-Yohkoh Coordinated Data Analysis Workshop, held March 3-7,
1997, at Goddard Space Flight Center.
@--------------------------------------------------------------------
Title: Multi-wavelength Observations of Transient Microwave
Brightenings in a Solar Active Region
Authors: Zhang, Jie; Gopalswamy, N.; Kundu, M. R.;
Schmahl, E. J.; Lemen, J. R.
Bibliographic Code: 1997SPD....28.0163Z
Abstract
We present multi-wavelength Very Large Array observations of two
transient microwave brightenings (TMBs) in the solar active region 7135.
The events were observed at 2 cm (spatial resolution ~ 2'') and 3.6 cm
(spatial resolution ~ 3'') with a temporal resolution of 3.3 s in a
time-sharing mode. Soft X-ray data (about 5'' spatial resolution) were
available from the Soft X-ray Telescope on board the YOHKOH satellite.
The 2 cm and 3.6 cm emission sources were very compact, located near the
footpoint of the magnetic loops seen in the X-ray images. The TMBs
traced out the three dimensional structure of the magnetic loops where
the transient brightenings occurred. For the two events reported in this
paper, the projected angular separation between the centroids of 2 and
3.6 cm source is about 2.3'' and 3.1'', respectively. We interpret the
spatial and temporal distributions as implying that the 2 and 3.6 cm
flux is mainly due to thermal gyro-resonance emmision. The 2 cm emission
seems to be at the 3rd gyro-harmonic coming from the 1800 G
gyro-resonance layer. The 3.6 cm emission seems to be at both the 2nd
and 3rd harmonics, originating from gyro-resonance layers with a
magnetic field of 1500 G and 1000 G, respectively. However, the two
gyro-resonance layers for 3.6 cm emission are not resolved with the
current spatial resolution. The estimated magnetic field gradient near
the footpoint of the magnetic loop is about 0.17 G km(-1) and 0.22 G
km(-1) for the two events.
@--------------------------------------------------------------------
Title: Microwave Radio Emission from Coronal X-ray Jets
Authors: Kundu, M. R.; Shibasaki, K.; Nitta, N.
Bibliographic Code: 1997SPD....28.0142K
Abstract
We report the first detection of microwave emission from coronal X-ray
jets using simultaneously obtained imaging data at 17 GHz (Nobeyama
Radioheliograph data) and in X-rays (Yohkoh/SXT data). We present
detailed results for one jet on the disk and another at the limb. The 17
GHz emission in the disk event originates from the base (a loop or a
system of loops) of the jet, and for the limb jet the microwave emission
comes from the base as well as from a part of the X-ray jet. We believe
that the collimated jet is optically thin at 17 GHz in most cases. We
have investigated more than two dozen jet events and found 17 GHz
emission in at least 70% of the cases. The 17 GHz emission is
unpolarized. We interpret the microwave emission as thermal, related to
the heating of the plasma responsible for the X-ray jet.
@--------------------------------------------------------------------
Title: Modeling of a Microwave Burst Emission
Authors: Preka-Papadema, P.; Alissandrakis, C. E.;
Dennis, B. R.; Kundu, M. R.
Bibliographic Code: 1997SoPh..172..233P
Abstract
@--------------------------------------------------------------------
Title: University of Maryland, Department of Astronomy,
College Park, Maryland 20742. Report for the period
1 Oct 1995 - 30 Sep 1996.
Authors: Kundu, M. R.
Bibliographic Code: 1997BAAS...29..232K
Abstract
@--------------------------------------------------------------------
Title: Radio and X-Ray Studies of a Coronal Mass Ejection
Associated with a Very Slow Prominence Eruption
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.; Enome, S.;
Lemen, J. R.; Akioka, M.; Lara, A.
Bibliographic Code: 1997ApJ...475..348G
Abstract
We report on the observations of an X-ray coronal mass ejection (CME)
with its three part structure: frontal loop, coronal cavity, and the
eruptive prominence core. The prominence core was observed in
microwaves, and the frontal loop was observed in X-rays. A coronal
volume much larger than that occupied by the prominence seems to be
affected by the eruption. Formation of an arcade structure was also
observed beneath the erupting prominence. X-ray enhancement at the
arcade persisted for several hours similar to long decay events. At the
apex of the arcade there was a bright knot, which we interpret as the
reconnection region from which the filament gets detached. We determined
the trajectories of the frontal loop and the prominence core and found
them to have very different characteristics. The CME showed an extremely
small acceleration, while the prominence had a linear motion in the
beginning followed by an exponential rise. However, during the several
hours of simultaneous observation, the prominence did not catch up with
the frontal loop. We determined the evolution of the CME mass, which
increased by a factor of 4 during our observations. We discuss the
implications of the observations in the general context of coronal mass
ejections.
@--------------------------------------------------------------------
Title: A Giant Prominence Eruption Observed by Nobeyama
Radioheliograph and YOHKOH Spacecraft
Authors: Gopalswamy, N.; Hanaoka, Y.; Kundu, M. R.;
Shibasaki, K.; Koshiishi, H.; Enome, S.;
Lemen, J. R.
Bibliographic Code: 1997IAUJD..19E...4G
Abstract
The results of an investigation of a giant prominence which erupted from
the northwest limb of the Sun on 1994 April 05, will be reported. The
event could be traced back to a large prominence of March 19, 1994 above
the east limb. The filament was located in the north-south direction
when it appeared on the disk. At about 23:00 UT on April 05, the
filament started slowly rising and then accelerated. The speed of the
prominence was was only 75 km s^{-1} when it reached a height of about
0.5 R_ odot above the surface. Preliminary examination shows that the
eruption caused a geomagnetic storm on April 07 at 20:00 UT. We study
the dynamical and physical properties of the erupting prominence and
obtain physical parameters of the prominence plasma. In X-rays, the
region of eruption was relatively faint. After the eruption, however,
there was a large void at the previous location of the prominence and an
arcade formed progressively spreading from south to north along the
limb. Based on the X-ray and radio observations, we determine the
characteristics of the pre- and post-eruption structures.
@--------------------------------------------------------------------
Title: A Multi-Wavelength Analysis of the February 6/7,
1997 Coronal Mass Ejection
Authors: Plunkett, S. P.; Gopalswamy, N.; Kundu, M.R.;
Howard, R.A.; Thompson, B.J.; Gurman, J.B.;
Lepping, R.P.; Hudson, H.S.; Nitta, N.; Hansoka, Y.;
Kosugi, T.; Burkepile, J.T.
Bibliographic Code: 1997ESASP.404..615P
Abstract
@--------------------------------------------------------------------
Title: Three Part Structure of a CME Revealed by X-Ray and
Microwave Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Lara, A.; Hanaoka, Y.;
Enome, S.; Lemen, J. R.; Akioka, M.
Bibliographic Code: 1997ASPC..111..393G
Abstract
@--------------------------------------------------------------------
Title: Radio and X-ray Imaging Observations of Solar Flares
and Coronal Transients
Authors: Kundu, M. R.
Bibliographic Code: 1996SoPh..169..389K
Abstract
We present a review of selected studies based upon simultaneous radio
and X-ray observations of solar flares and coronal transients. We use
primarily the observations made with large radio imaging instruments
(VLA, BIMA, Nobeyama, and Nançay) along with Yohkoh/SXT and HXT
and CGRO experiments. We review the recent work on millimeter imaging of
solar flares, microwave and hard X-ray observations of footpoint
emission from flaring loops, metric type IV continuum bursts, and
coronal X-ray structures. We discuss the recent studies on thermal and
nonthermal processes in coronal transients such as XBP flares, coronal
X-ray jets, and active region transient brightenings.
@--------------------------------------------------------------------
Title: Radio Continuum and Type III Bursts Associated with
Coronal X-Ray Structures
Authors: Raulin, J. P.; Kundu, M. R.; Nitta, N.; Raoult, A.
Bibliographic Code: 1996ApJ...472..874R
Abstract
In this paper, we report the detection of a metric continuum burst
source at the top of a coronal loop observed in soft X-rays. The
continuum burst was probably a flare continuum that lasted more than 1
hr. This is the first observation of such metric continuum emission
produced by energetic electrons with high-spatial resolution imaging
instruments in both X-rays and radio. The nonthermal radio emission
appears to be associated with the rupture of a part of the loop top and
the ejection of soft X-ray plasma at the top of the coronal loop. We
have also identified X-ray coronal structures in which type III emitting
electron beams propagate. The metric continuum is most likely caused by
second-harmonic plasma emission, and the electron density in the soft
X-ray structure where type Ills are observed is close to the critical
plasma density derived from radio observations.
@--------------------------------------------------------------------
Title: Observation and model calculations of sunspot ring
structure at 8.46GHz
Authors: Gopalswarmy, N.; Raulin, J. P.; Kundu, M. R.;
Hildebrandt, J.; Krueger, A.; Hofmann, A.
Bibliographic Code: 1996A&A...316L..25G
Abstract
We present Very Large Array (VLA) observations of AR 7542 which
demonstrate the existence of definite ring and horse-shoe structures of
a sunspot in intensity (I) and polarization (V) at 8.46GHz (3.5cm
wavelength) and compare them with model calculations of gyroresonance
radiation. The VLA measurements have been made on three different days
in July 1993 when AR 7542 was at three different longitudes which allows
us to study the effect of viewing angle on sunspot-associated microwave
emission. Model calculations of gyroresonance radiation have been
carried out using a modified dipole model corresponding to the observed
photospheric magnetic field strength and average temperature/electron
density distributions consistent with soft X-ray and EUV observations
(for the lower atmosphere) as well as theoretical assumptions (for the
corona). The calculated I and V maps were found to be generally
consistent with the radio observations. We obtain information on the
magnetic scale length in vertical and horizontal directions above the
sunspot and about the distribution of other plasma parameters
(temperature, density) inside the radio source region.
@--------------------------------------------------------------------
Title: Yohkoh/SXT observations of a coronal mass ejection
near the solar surface
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.;
Lemen, J. R.; Akioka, M.
Bibliographic Code: 1996NewA....1..207G
Abstract
We report the observations of a coronal mass ejection (CME) using the
Soft X-ray Telescope on board the Yohkoh Mission. The CME had the
familiar three part structure (frontal loop, prominence core and a
cavity). The erupting prominence was observed by the Nobeyama
radioheliograph. We were able to determine the mass of the CME (2.6
× 1014 g) from X-ray observations which seems to be at
the lower end of the range of CME masses reported before from white
light observations. This is the first time the mass of a CME has been
determined from X-ray observations. The height of onset of the CME was
0.3R&sun;. The CME moved much faster than the erupting
prominence while its acceleration was smaller than that of the erupting
prominence.J. Leonard Culhane
@--------------------------------------------------------------------
Title: A Model for Active Region Emission at Centimeter
Wavelengths
Authors: Nindos, A.; Alissandrakis, C. E.; Gelfreikh, G. B.;
Kundu, M. R.; Dere, K. P.; Korzhavin, A. N.;
Bogod, V. M.
Bibliographic Code: 1996SoPh..166...55N
Abstract
We present multi-frequency observations and model computations of the
microwave emission of a solar active region. The radio observations were
obtained with the RATAN-600 at several wavelengths between 0.8 and 31.6
cm and with the VLA at 6 and 20 cm. The active region was also observed
in the EUV O Iv lines by the HRTS instrument aboard the Space Shuttle
Spacelab-2 mission. These lines are formed in the chromosphere-corona
transition region and their intensity ratio is sensitive to pressure.
Photospheric magnetograms provided both the longitudinal and the
transverse component of the magnetic field. The microwave observations
were checked against model computations taking into account both the
free-free and the gyro-resonance emission mechanisms and using the
pressure data from the O IV lines. The magnetic field was computed
through constant-alpha force-free extrapolations of the longitudinal
photospheric field. We computed both the flux from 2 to 20 cm and the
spatial structure of the microwave emission at 6 and 20 cm. The
comparison of the computed and observed flux spectra allowed us to
estimate the magnetic field strength at the base of the transition
region and in the low corona, as well as the values of the conductive
flux and the height of the base of the transition region. The model maps
at 6 cm and 20 cm showed that alpha was not constant above the active
region; the same conclusion was reached on the basis of the photospheric
observations. The use of pressure measurements allowed us to identify
microwave structures which were determined by pressure enhancements. At
6 cm the computations confirmed the fact that the magnetic field is the
principal factor that determines the structure of sunspot-associated
sources and showed that the effect of pressure variations was small.
Pressure variations were more important at 20 cm, where the peak of the
emission was associated with the sunspot and a diffuse component was
associated with the plage which had an average pressure higher by a
factor of 1.54 than the sunspot.
@--------------------------------------------------------------------
Title: Radio and X-ray manifestations of a bright point
flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.;
Lemen, J. R.
Bibliographic Code: 1996AIPC..374..408G
Abstract
We have found remarkably different manifestations of a bright point
flare in X-ray and radio (microwave) wavelengths, unlike previous
observations. In X-rays, the BP flare was relatively simple while in
radio, the bright point flare had a large scale component and a
transient moving component. The large scale structure may be the radio
counterpart of large scale structures sometimes seen during X-ray BP
flares. The transient component was also compact and moved away from the
location of the X-ray BP flare with a speed of ~60 km s-1. The compact
source also showed fast time structure which suggests nonthermal
emission mechanism for the transient sources.
@--------------------------------------------------------------------
Title: Coronal X-Ray Structures and Metric Radio Type III
and IV Bursts
Authors: Kundu, M. R.; Raulin, J.-P.; Nitta, N.; Raoult, A.
Bibliographic Code: 1996AAS...188.8609K
Abstract
Over the past several years Yohkoh/SXT experiments have led to the
discovery of many new and interesting dynamic phenomena. Of particular
interest are the flaring X-ray bright points (XBPs), X-ray jets, and
flare associated plasmoids and other ejecta. We have looked for evidence
of nonthermal processes occurring in these X-ray events, using radio
bursts of spectral types III and IV. We have used positional information
of metric radio bursts using the Nancay (France) Radioheliograph in the
frequency range 150-450 MHz simultaneously with the Yohkoh experiments.
We have evidence of nonthermal type III burst emission in the meter wave
range in association with flaring XBPs and certain classes of X-ray
jets. We have detected metric structures, namely flaring loops (possibly
plasmoids) and other ejecta. The implications of these findings will be
discussed in terms of our understanding of radio bursts of different
spectral types.
@--------------------------------------------------------------------
Title: Large Scale Features of the Radio Sun
Authors: White, S. M.; Gary, D. E.; Kundu, M. R.
Bibliographic Code: 1996AAS...188.7907W
Abstract
We present full-disk images of the Sun at 5 GHz made by observing 26
different fields with the Very Large Array and combining them using
mosaicking techniques. The resulting image combines sensitivity to
large-scale structures with good resolution. Full-disk images at 0.33,
1.4 and 17 GHz, a high-resolution magnetogram and a soft X-ray image are
compared with the 5 GHz image to investigate the physical properties of
large-scale features.
@--------------------------------------------------------------------
Title: Millimeter Observations of a B5.6 Flare
Authors: Raulin, J.-P.; White, S. M.; Kundu, M. R.;
Silva, A. V. R.; Shibasaki, K.
Bibliographic Code: 1996AAS...188.4503R
Abstract
We present millimeter imaging observations of a B5.6 flare which occured
on 1994 August 16 in the active region AR 7765. The BIMA interferometer
and the Nobeyama radioheliograph observed both the impulsive phase and
the thermal phase of the flare emission. The 3.5 mm maps obtained with
BIMA allowed us to determine the location of the radio source and its
properties at different phases of the flare evolution. In X-ray
wavelengths the impulsive phase was detected by the first two channels
of BATSE (25-50 keV, 50-100 keV); although YOHKOH/SXT did not observe
the impulsive phase, it was possible to image the post-flare loop in
soft X-rays. We compare the images of the flare at different wavelengths
and discuss the relevance of millimeter emission in the context of flare
models.
@--------------------------------------------------------------------
Title: Polarization of Microwaves Emitted From A Bipolar
Active Region
Authors: Lee, Jeongwoo; White, Stephen; Gopalswamy, N.;
Kundu, M. R.
Bibliographic Code: 1996AAS...188.3603L
Abstract
High resolution microwave maps of a complex bipolar active region,
AR6615, were obtained using the VLA on 1991 May 7 at three frequencies,
4.9 GHz, 8.4 GHz, and 15 GHz. Comparison of this microwave observation
with Big Bear magnetogram suggests that inversion and depolarization of
microwave emission must have occurred at different sites of the active
region depending on frequency. For quantitative interpretation of the
polarization data, we constructed the coronal magnetic fields above the
active region using the potential field extrapolation. In the model, we
identified the quasi-transverse (QT) surface across which change of the
polarization may occur. It is found that the required topology of the QT
surface to explain the observed polarization is correctly predicted by
the potential field model, although the locations of the 15 GHz
gyroresonance sources required a nonlinear force-free field
extrapolation in part. With the calculation of the mode coupling
coefficient along the QT surface, we were able to locate the region of
depolarization above a strong sunspot, consistent with the observation.
We also discuss the appropriate theoretical gyroresonant opacity for
waves propagating perpendicular to the magnetic fields, as needed to
understand the observed polarization across the magnetic neutral line.
Applicability of the present results to study of the coronal magnetic
structure above complex bipolar regions, in general, is briefly
discussed.
@--------------------------------------------------------------------
Title: A Multi Wavelength Study of Active Region
Development
Authors: Lara, A.; Gopalswamy, N.; Kundu, M. R.;
Perez-Enriquez, R.; Koshiishi, H.; Enome, S.
Bibliographic Code: 1996AAS...188.3601L
Abstract
We report on a study of the evolution of several active regions during
1993 April 17-28 using data obtained at multiple wavelengths that probe
various heights of the active region corona. We use simultaneous
microwave (1.5 and 17 GHz) and Soft X-ray images obtained by the Very
Large Array (VLA), the Nobeyama Radio Heliograph (NRH) and the Soft
X-ray Telescope (SXT) on board the Yohkoh spacecraft. We also use
photospheric magnetograms from Kitt Peak National Observatory to study
the development of Solar Active Regions. We have followed the
development of various observed parameters such as brightness
temperature and polarization using radio images. The X-ray data were
used to track the development of density and temperature of active
regions. Using the fact that the quiet active region radiation is
thermal and adopting proper emission mechanism at each frequency domain,
we construct a consistent picture for the three dimensional structure of
the active regions. Particular attention has been paid to the mode
coupling observed at 17 GHz while the active regions crossed the solar
disk.
@--------------------------------------------------------------------
Title: Tracking Type III and Type II Solar Radio Bursts
from Metric to Hectometric Wavelengths using
Ground-based and Space-borne Observations
Authors: Gopalswamy, N.; Kundu, M. R.; Kaiser, M. L.;
Kahler, S. W.; Kondo, T.; Isobe, T.; Akioka, M.
Bibliographic Code: 1996AAS...188.1908G
Abstract
There exists a controversy regarding the origin of coronal and
interplanetary (IP) shocks. Present observations shows that coronal
shocks are associated with flares while the IP shocks are associated
with coronal mass ejections (CMEs). An important question in this
connection is whether the IP shocks are extensions of the coronal shocks
or they are independently driven by CMEs. The coronal shocks have
traditionally been inferred from metric type II radio bursts. The
ionospheric cut-off around 20 MHz had been a hurdle in arriving at a
firm conclusion regarding the continuation of type II bursts to
frequencies lower than the ionospheric cut off. The WAVES experiment on
board the WIND spacecraft has essentially removed this hurdle so that we
are able to track metric radio bursts to hectometric wavelengths. We
have identified about two dozen type II bursts observed by the Hiraiso
Radio Spectrograph (HiRAS) after the launch of the WIND satellite. Most
of these type II bursts were accompanied by type III bursts. We have
positively identified the solar flares associated with all the events.
When we examined the WIND Radio and Plasma waves (WAVES) data, we found
the following: (i) Most of the metric (Hiraiso) type III bursts have
counterparts in the WAVES data; (ii) None of the metric type II bursts
have counterparts in the WAVES data. This result suggest that coronal
shocks responsible for metric type II bursts are blast waves which decay
rapidly within the inner corona while the electron beams producing type
III bursts continue to propagate to the IP medium.
@--------------------------------------------------------------------
Title: A model of the atmosphere above a sunspot from radio
observations
Authors: Zlotnik, E. Ya.; Kundu, M. R.; White, S. M.
Bibliographic Code: 1996R&QE...39..255Z
Abstract
The results of VLA observations of an unusual source of microwave
radiation, associated with the sunspot NOAA 7789 on October, 15, 1994,
are presented. The fine structure of the source, which is a ring
structure in intensity and polarization at frequencies 4.5 and 8.0 GHz,
is discussed. It is shown that the features observed can be explained by
a thermal cyclotron mechanism if the magnetic field is approximated by a
vertical dipole buried under the photosphere, but the spatial
distributions of kinetic temperature and electron density in the
atmosphere above the sunspot differ considerably from the standard
model. A two-dimensional source model (the dependences of the parameters
on the height and distance from the center of the sunspot), which fits
the observations at the above frequencies, is evolved. The principal
physical result is that the data observed are explainable by the
presence of an unexpectedly dense cool plasma in the atmosphere over the
center of the umbra.
@--------------------------------------------------------------------
Title: Detection of Large-Scale Radio Structure and Plasma
Flow during a Solar Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.;
Lemen, J. R.
Bibliographic Code: 1996ApJ...457L.117G
Abstract
We report on the detection of a large-scale radio structure and plasma
flow associated with a bright point flare observed on 1993 July 11. The
bright point (BP) flare was simultaneously imaged by the Nobeyama
radioheliograph at 17 GHz and the Soft X-Ray Telescope on board the
Yohkoh mission. The microwave emission consists of a large-scale
structure and a compact moving source. The large-scale component seems
to be the radio counterpart of large-scale loop structures sometimes
observed in association with BP flares in X-rays. The compact source
moved from the location of the X-ray BP flare with a speed of about 60
km s-1, which suggests a plasma flow. Spatial comparison between X-ray
and radio data shows that the BP flare had different manifestations in
the two wavelength domains. The emission peaks in the two wavelength
domains did not coincide, which suggests cool plasma flow along the
large-scale radio structure. We were able to determine the temperature
and emission measure of the BP flare plasma from the X-ray data, and
thus we computed the expected radio flux from the X-ray--emitting
plasma. We found that the computed radio flux was much smaller than the
total observed radio flux.
@--------------------------------------------------------------------
Title: Metric Type III bursts associated with soft X-ray
jets.
Authors: Raulin, J. P.; Kundu, M. R.; Hudson, H. S.;
Nitta, N.; Raoult, A.
Bibliographic Code: 1996A&A...306..299R
Abstract
From soft X-ray and metric radio observations with high temporal and
spatial resolution, we show that electron acceleration in the form of
Type III bursts occurs in association with coronal jets observed by the
Yohkoh soft X-ray telescope. The excellent correspondence between the
positions of the radio sources observed at different frequencies and the
X-ray jets strongly suggests that electron beams propagate along the
relatively dense paths formed by the jets. Assuming a constant
temperature for the jets, one can estimate the electron density from the
soft X-ray measurements. These computed electron densities agree well
with the values derived from Type III bursts produced by the plasma
emission process. The observations are consistent with the idea that
strong particle acceleration accompanies magnetic reconnection in these
events as well as in solar flares.
@--------------------------------------------------------------------
Title: Detection of Nonthermal Radio Emission from Coronal
X-ray Jets
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.;
Hudson, H. S.; Raoult, A.; Shibata, K.; Shimojo, M.
Bibliographic Code: 1996mpsa.conf..445K
Abstract
@--------------------------------------------------------------------
Title: Three part structure of a CME revealed by X-ray and
microwave observations.
Authors: Gopalswamy, N.; Kundu, M. R.; Lara, A.; Hanaoka, Y.;
Enome, S.; Lemen, J. R.; Akioka, M.
Bibliographic Code: 1996ASPC..111..393G
Abstract
The authors present X-ray (Yohkoh/SXT) and microwave (17 GHz Nobeyama)
observations of the 1993 July 10 - 11 CME. During this event, all the
substructures of a classical CME are revealed: frontal loop in X-rays,
prominence core in microwaves, dark cavity between prominence and
frontal loop in X-rays, and arcade structure beneath the prominence in
X-rays.
@--------------------------------------------------------------------
Title: Nonthermal Radio Emission from Coronal X-ray Jets
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.;
Hudson, H. S.; Raoult, A.
Bibliographic Code: 1996ASPC...93..375K
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of a Solar Active Region at 6.2 and
3.5 CM Wavelength Compared with Model Calculations
Authors: Hildebrandt, J.; Kruger, A.; Gopalswamy, N.;
Raulin, J.-P.; Kundu, M. R.
Bibliographic Code: 1996ASPC...93..369H
Abstract
@--------------------------------------------------------------------
Title: The Radio Outburst of eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Drake, S. A.;
Kundu, M. R.
Bibliographic Code: 1996ASPC...93...59W
Abstract
@--------------------------------------------------------------------
Title: A Search for Rotational Modulation in the EUV
Emission from AB Doradus
Authors: White, S. M.; Lim, J.; Rucinski, S. M.; Roberts, C.;
Kilkenny, D.; Ryan, S. G.; Prado, P.; Kundu, M. R.
Bibliographic Code: 1996aeu..conf..165W
Abstract
@--------------------------------------------------------------------
Title: VLA and YOHKOH Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Raulin, J.-P.; Kundu, M. R.;
Nitta, N.; Lemen, J. R.; Herrmann, R.; Zarro, D.;
Kosugi, T.
Bibliographic Code: 1995ApJ...455..715G
Abstract
A major solar flare (X-ray importance M1.5 and optical importance SB)
was fully observed by the Very Large Array and the Yohkoh mission on
1993 April 22. Both thermal and nonthermal emissions were observed in
radio. In soft X-rays, the flare was confined to a compact region in an
arcade. In hard X-rays, there were two prominent footpoints, coincident
in projection with the soft X-ray footpoints and located on either side
of the magnetic neutral line inferred from photospheric magnetograms The
Yohkoh Bent Crystal Spectrometer (B CS) data provided important context
information which was helpful in cross-checking the quantitative
agreement between the radio and X-ray data. The microwave spectrum
peaked around 10 GHz and showed Razin suppression in the beginning.
Later on, the low-frequency spectral index dropped to a value of 2,
suggesting thermal emission. The VLA images of the flare at 1.5 GHz show
that the flare emission started as a single source above one footpoint;
later on, the emission centroid moved toward the soft X-ray structure to
finally become cospatial with the latter. The two locations of the 20 cm
source corresponded to nonthermal (footpoint source) and thermal (source
cospatial with the soft X-ray structure) emissions. We performed
temperature and emission measure analysis of the X-ray data (SXT, BCS,
and HXT) and used them as input to determine the expected radio
emission. While there is morphological agreement between the radio and
soft X-ray structures in the thermal phase, the 20 cm brightness
temperature shows quantitative agreement with temperature derived from
the BCS data. We were able to identify three emission mechanisms
contributing to the 20 cm radio emission at different times without any
ad hoc assumption regarding emission mechanisms. Razin-suppressed
nonthermal gyroresonance emission, plasma emission, and thermal
free-free emission seem to be operating and are found to be consistent
with the plasma parameters derived from the X-ray data. The magnetic
field structure in the flaring region showed differences before and
after the flare as traced b soft X-ray structures in the flaring region
and confirmed by 20 cm radio images. The superhot component with a
temperature of 32 MK was observed in hard X-ray images and in light
curves during the impulsive phase of the flare with possible radio
signatures at 20 cm wavelength. We derived the physical parameters of
the flaring plasma, the magnetic field, and the characteristics of
nonthermal particles in the flaring region.
@--------------------------------------------------------------------
Title: Microwave and Hard X-Ray Observations of Footpoint
Emission from Solar Flares
Authors: Kundu, M. R.; Nitta, N.; White, S. M.; Shibasaki, K.;
Enome, S.; Sakao, T.; Kosugi, T.; Sakurai, T.
Bibliographic Code: 1995ApJ...454..522K
Abstract
We investigate radio and X-ray imaging data for two solar flares in
order to test the idea that asymmetric precipitation of nonthermal
electrons at the two ends of a magnetic loop is consistent with the
magnetic mirroring explanation. The events we present were observed in
1993 May by the HXT and SXT X-ray telescopes on the Yohkoh spacecraft
and by the Nobeyama 17 GHz radioheliograph. The hard X-ray images in one
case show two well-separated sources; the radio images indicate
circularly polarized, nonthermal radio emission with opposite polarities
from these two sources, indicating oppositely directed fields and
consistent with a single-loop model. In the second event there are
several sources in the HXT images which appear to be connected by soft
X-ray loops. The strongest hard X-ray source has unpolarized radio
emission, whereas the strongest radio emission lies over strong magnetic
fields and is polarized. In both events the strongest radio emission is
highly polarized and not coincident with the strongest hard X-ray
emission. This is consistent with asymmetric loops in which the bulk of
the precipitation (and hence the X-ray emission) occurs at the weaker
field footpoint.
@--------------------------------------------------------------------
Title: Microwave proxies for sunspot blocking and total
irradiance
Authors: Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1995JGR...10019851S
Abstract
The microwave flux of the Sun is responsive to the same conditions that
produce magnetically structured radiation at visible and X ray
wavelengths, and so the solar flux at high radio frequencies such as
2800 MHz (10.7 cm) has been used as a proxy for solar optical
variations. We have previously found that the microwave flux time series
show spectral variations that provide useful proxy information for total
irradiance, and we have extended our analysis of the daily solar fluxes
from Toyokawa Observatory at 1000, 2000, 3750, and 9400 MHz, in addition
to the Ottawa 2800-MHz flux, for the years 1980-1989. An essential
ingredient in our analysis is the extraction of the
rotationally-modulated microwave component, which differs from the ``S
component'' as recently defined in the literature. The
rotationally-modulated fraction of the emission contains a significant,
often dominant, contribution from gyroresonance emission, whereas the S
component, as defined by the excess above the cycle minimum level,
usually does not.
This allows us to distinguish plage-associated
emission from spot-associated emission in the time series of microwave
flux. We show that in combination, the microwave fluxes for 1000-9400
MHz, which span the spectral peak of spot-associated emission, provide a
very good proxy both the active cavity radiometer irradiance monitor
(ACRIM) total irradiance and the sunspot-blocked component of the
irradiance, even without optical sunspot observations. Over the
1984-1989 period, this proxy has a weighted correlation with ACRIM of
95%, and an RMS deviation from the total irradiance of 0.27
w/m2, slightly better than the deviation (0.35
w/m2) found using optical data.
@--------------------------------------------------------------------
Title: The Radio Properties of Solar Active Region Soft
X-Ray Transient Brightenings
Authors: White, S. M.; Kundu, M. R.; Shimizu, T.;
Shibasaki, K.; Enome, S.
Bibliographic Code: 1995ApJ...450..435W
Abstract
We present the results of a search for radio emission from active-region
transient brightenings identified in Yohkoh soft X-ray telescope
observations of active region AR 7260. We present detailed observations
of four events in which 17 GHz radio emission is clearly detected in
observations by the Nobeyama radioheliograph. The time profiles of the
17 GHz data are very similar to those of the soft X-ray fluxes, and the
17 GHz flux is very close to that expected from plasma with the
temperature and emission measure derived for the soft X-ray emitting
material from filter ratios. No impulsive nonthermal radio emission was
detected from any of the four events, although each was at least GOES
class B 1 in soft X-rays. Weak hard X-rays may have been detected by
GRO/BATSE from the strongest of the events, but not from two others.
These negative results leave open the possibility that there is a
difference between active region transient brightenings and solar
flares, in that the former do not convert a significant amount of the
released energy into accelerated electrons. However, confirmation of
this hypothesis will require a larger sample of events.
@--------------------------------------------------------------------
Title: Detection of Nonthermal Radio Emission from Coronal
X-Ray Jets
Authors: Kundu, M. R.; Raulin, J. P.; Nitta, N.;
Hudson, H. S.; Shimojo, M.; Shibata, K.; Raoult, A.
Bibliographic Code: 1995ApJ...447L.135K
Abstract
We report the detection of a type III burst in association with a
dynamic X-ray coronal jet observed by Yohkoh/SXT. The type III burst
observed with the Nancay (France) multifrequency radioheliograph is
spatially and temporally coincident with the X-ray jet. The radio
locations at different frequencies (236.6 and 164 MHz) are aligned along
the length of the jet. The observation of the type III burst in
association with the X-ray jet implies the acceleration of electrons to
several tens of keV, along with the heating responsible for the
production of soft X-rays. This association implies the existence of
open field lines in dense coronal structures identified on the Sun's
disk. This is the first observation of dense coronal structures on the
disk, along which type III emitting nonthermal electrons propagate. We
find that this structure begins to form before the type III emission. At
the time of the type III burst we estimate a density of 6--10 x 108 cm-3
for a temperature of ~5--6 MK at an altitude of 20,000 km.
@--------------------------------------------------------------------
Title: Observations of Continuum and - Emission from Eta
Carinae at a Wavelength of 3 CM
Authors: Duncan, R. A.; White, S. M.; Lim, J.; Nelson, G. J.;
Drake, S. A.; Kundu, M. R.
Bibliographic Code: 1995RMxAC...2...23D
Abstract
@--------------------------------------------------------------------
Title: Metric type III bursts from a flaring X-ray bright
point near an active region
Authors: Kundu, M. R.; Raulin, J. P.; Pick, M.; Strong, K. T.
Bibliographic Code: 1995ApJ...444..922K
Abstract
X-ray bright points (XBPs) are known to show variability on a number of
timescales, including impulsive X-ray brightenings. The relationship
between these XBP 'flares' and normal flares is poorly known. A
fundamental question is whether nonthermal acceleration of particles
takes place in XBP flares. We address this issue by seravhing for
nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh/SXT data. Unequivocal evidence for type III-like
radio bursts usually attributed to beams of nonthermal electrons on open
field lines was found recently by Kundu et al. This suggests that XBP
flares are similar to normal flares and can indeed accelerate nonthermal
populations of energetic particles. Here we provide further evidence of
metric type III bursts from flaring XBPs located near active regions.
@--------------------------------------------------------------------
Title: Nouthermal Radio Emission From Coronal X-Ray Jets
Authors: Raulin, J. P.; Kundu, M. R.; Hudson, H. S.;
Nitta, N.; Raoult, A.
Bibliographic Code: 1995SPD....26.1318R
Abstract
@--------------------------------------------------------------------
Title: Radio Counterpart of an X-ray Bright Point Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Hanaoka, Y.; Enome, S.;
Lemen, J. R.
Bibliographic Code: 1995SPD....26.1317G
Abstract
@--------------------------------------------------------------------
Title: Spatially resolved Millimeter (86 GHz), Microwave
(17 GHz) and X-Ray Observations of the 17 August 94
flare
Authors: Silva, A. V. R.; Lin, R. P.; de Pater, I.;
White, S. M.; Kundu, M. R.
Bibliographic Code: 1995SPD....26..804S
Abstract
@--------------------------------------------------------------------
Title: The Magnetic Field Over an Isolated Symmetric
Sunspot
Authors: White, S. M.; Kundu, M. R.; Zlotnik, E. Ya.;
Zheleznyakov, V. V.; Nitta, N.
Bibliographic Code: 1995SPD....26..718W
Abstract
@--------------------------------------------------------------------
Title: Intense radio outburst from the supermassive star
Eta Carinae
Authors: Duncan, R. A.; White, S. M.; Lim, J.; Nelson, G. J.;
Drake, S. A.; Kundu, M. R.
Bibliographic Code: 1995ApJ...441L..73D
Abstract
On five occasions between 1992 June 29 and 1994 May 3, we have used the
Australia Telescope Compact Array (ATCA) to image Eta Carinae at a
wavelength of 3 cm and a resolution of 1 arcsec. These observations have
revealed remarkable activity. Since 1992 June, the total flux density
has increase from 0.8 to 2.2 Jy, and the original single compact source
has grown to a complex of sources spread over an area of about 16 sq
arcsec. Strong hydrogen recombination-line spectral emission has
appeared at the site of the strongest of these new sources. This
recombination emission has the largest spectral width ever observed from
a star, +/- 250 km/s, and reveals gas with turbulent velocities as great
as 250 km/s approaching us at an average velocity of about 200 km/s. We
believe that this radio outburst has been caused by a more than
threefold increase of ultraviolet luminosity, and consequent ionization
of previously neutral gas clouds.
@--------------------------------------------------------------------
Title: Nobeyama Radio Observatory report, no. 361: The
radio properties of solar active region soft x-ray
transient brightenings
Authors: White, S. M.; Kundu, M. R.; Shimizu, T.;
Shibasaki, K.; Enome, S.
Bibliographic Code: 1995STIN...9529098W
Abstract
We present the results of a search for radio emission from active-region
transient brightenings identified in Yohkoh Soft X-ray Telescope
observations of active region AR 7260. We present detailed observations
of four events in which 17 GHz radio emission is clearly detected in
observations by the Nobeyama Radioheliograph. The time profiles of the
17 GHz data are very similar to those of the soft X-ray fluxes, and the
17 GHz flux is very close to that expected from plasma with the
temperature and emission measure derived for the soft X-ray-emitting
material from filter ratios. No impulsive nonthermal radio emission was
detected from any of the 4 events, although each was at least GOES class
B1 in soft X-rays. Weak hard X-rays may have been detected by GRO/BATSE
from the strongest of the events, but not from two others. These
negative results leave open the possibility that there is a difference
between active region transient brightenings and solar flares, in that
the former do not convert a significant amount of the released energy
into accelerated electrons. However, confirmation of this hypothesis
will require a larger sample of events.
@--------------------------------------------------------------------
Title: Surprises in the Radio Signatures of CMEs
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1995LNP...444..223G
Abstract
@--------------------------------------------------------------------
Title: Characteristics of Two Simple Microwave Bursts
Authors: Kundu, M. R.; White, S. M.; Nitta, N.; Shibasaki, K.;
Enome, S.
Bibliographic Code: 1995LNP...444...75K
Abstract
@--------------------------------------------------------------------
Title: Polarization features of solar radio emission and
possible existence of current sheets in active
regions
Authors: Gopalswamy, N.; Zheleznyakov, V. V.; White, S. M.;
Kundu, M. R.
Bibliographic Code: 1994SoPh..155..339G
Abstract
We show that it is possible to account for the polarization features of
solar radio emission provided the linear mode coupling theory is
properly applied and the presence of current sheets in the corona is
taken into account. We present a schematic model, including a current
sheet that can explain the polarization features of both the low
frequency slowly varying component and the bipolar noise storm
radiation; the two radiations face similar propagation conditions
through a current sheet and hence display similar polarization behavior.
We discuss the applications of the linear mode coupling theory to the
following types of solar emission: the slowly varying component, the
microwave radio bursts, metric type U bursts, and bipolar noise storms.
@--------------------------------------------------------------------
Title: Transient microwave brightenings in solar active
regions: Comparison between VLA and YOHKOH
observations
Authors: Gopalswamy, N.; Payne, T. E. W.; Schmahl, E. J.;
Kundu, M. R.; Lemen, J. R.; Strong, K. T.;
Canfield, R. C.; de La Beaujardiere, J.
Bibliographic Code: 1994ApJ...437..522G
Abstract
We report observations of transient microwave (2 cm) brightenings and
their relationship with brightenings in soft X-rays. The peak flux of
the microwave brightenings observed by the Very Large Array (VLA) is
smaller than the previously reported fluxes by two orders of magnitude.
The microwave sources were highly polarized (up to 100%) and were
situated on the periphery of a sunspot umbra. Among the many transients
observed in X-rays by Yohkoh, two were observed simultaneously in
microwaves. The microwave sources were found to be closer to the umbra
of the sunspot than were the X-ray loops. It seems that the microwave
sources are located at the footpoints of the looplike X-ray transients.
Using the combined VLA, Yohkoh, and Mees data set, we determine the
physical parameters of the loop in which the brightenings occur. We find
that an increase in emission measure accompanied by small-scale heating
can account for the X-ray brightening. The microwave emission can be
interpreted as thermal gyroresonance or nonthermal gyrosynchrotron
processes during the X-ray brightening. The magnetic field in the
microwave-source region is found to be 1200-1800 G. The observations
also provide evidence for temperature gradient in the coronal loops.
@--------------------------------------------------------------------
Title: Detection of 17 GHz radio emission from X-ray-bright
points
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.
Bibliographic Code: 1994ApJ...431L.155K
Abstract
Using observations made with the Nobeyama radio heliograph (NRH) at 17
GHz and the Yohkoh/SXT experiment, we report the first detection of 17
GHz signatures of coronal X-ray-bright points (XBPs). This is also the
first reported detection of flaring bright points in microwaves. We have
detected four BPs at 17 GHz out of eight identified in SXT data on 1992
July 31, for which we looked for 17 GHz emission. For one XBP located in
a quiet mixed-polarity region, the peak times at 17 GHz and X-rays are
very similar, and both are long-lasting-about 2 hr in duration. There is
a second BP (located near an active region) which is most likely flaring
also, but the time profiles in the two spectral domains are not similar.
The other two 17 GHz BPs are quiescent with fluctuations superposed upon
them. For the quiet region XBP, the gradual, long-lasting, and
unpolarized emission suggests that the 17 GHz emission is thermal.
@--------------------------------------------------------------------
Title: Evolution of an Active Region and Flare Productivity
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.;
Bruner, M.; Sakao, T.; Kosugi, T.
Bibliographic Code: 1994kofu.symp..353K
Abstract
We have studied the evolution of an active region (AR 7515) in terms of
flare productivity. This region appears at the east limb on May 23, 1993
and then continues its onward march across the disk. We follow its
evolution until June 2. This region produces many small flares. We study
the topology, both magnetic and structural of the neighboring regions as
observed at 17 GHz by the Nobeyama Radio Heliograph (NRH) and the
Yohkoh/SXT to find their effects on the flare-producing AR. We
investigate the spatial structure of the flaring region from 17 GHz and
SXT maps during various times of the impulsive and decay phase, to
understand the difference in the flaring region spatial structure during
the preflare, impulsive and decay phases. In general, the maps made
during these phases show several loops. We try to relate these flaring
loops with the preflare active region structure.
@--------------------------------------------------------------------
Title: Study of Active Region Magnetic Field Structures
Using VLA Radio, YOHKOH X-ray and MEES Optical
Observations
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.;
Lemen, J. R.; Strong, K. T.; Canfield, R. C.;
de La Beaujardiere, J.
Bibliographic Code: 1994kofu.symp..347G
Abstract
We report on the observation of compact magnetic flux tubes from the
boundary between the umbra and penumbra of a large sunspot in AR 7135 on
April 24, 1992. The structure and geometry of one such flux tube was
determined using the coordinated observations obtained by the Very Large
Array, the Yohkoh Soft X-ray Telescope and the Mees Solar Observatory.
From radio observations we infer that the magnetic field of the flux
tube at the spot-side footpoint is ~ 1300-1800 G.
@--------------------------------------------------------------------
Title: Metric Type III Bursts from Flaring X-ray Bright
Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Harvey, K. T.;
Kane, S. R.; White, S. M.; Hudson, H. S.
Bibliographic Code: 1994kofu.symp..343K
Abstract
X-ray bright points (XBP's) are known to show variability on a number of
timescales, including impulsive X-ray brightenings. The relationship
between these XBP ``flares'' and normal solar flares is poorly known. A
fundamental question is whether nonthermal acceleration of particles
takes place in XBP flares. We address this issue by searching for
nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh/SXT data. Unequivocal evidence for type-III-like
radio bursts, usually attributed to beams of nonthermal electrons on
open field lines, is found. This suggests that XBP flares are similar to
normal flares and can indeed accelerate nonthermal populations of
energetic particles.
@--------------------------------------------------------------------
Title: Multiwavelength Observations of a Solar Flare
Authors: White, S. M.; Silva, A.; de Pater, I.; Lin, R. P.;
Gary, D. E.; Hudson, H. S.; Doyle, J. G.;
Hagyard, M. J.; Kundu, M. R.
Bibliographic Code: 1994kofu.symp..203W
Abstract
@--------------------------------------------------------------------
Title: Observation of 17 GHz Radio Emission from X-ray
Bright Points
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.
Bibliographic Code: 1994kofu.symp...79K
Abstract
Using observations made with the Nobeyama radio heliograph (NRH) at 17
GHz and the Yohkoh/SXT experiment, we report the first detection of 17
GHz signatures of coronal X-ray bright points (XBP's). This is also the
first reported detection of flaring bright points in microwaves. We have
detected four BP's at 17 GHz out of eight observed by SXT on July 31,
1992, for which we looked for 17 GHz emission. For one XBP located in a
quiet mixed-polarity-region, the peak times at 17 GHz and X-rays are
very similar, and both are long lasting -- at least 6 hours in duration.
There is a second BP (located near an active region) which is most
likely flaring also, but the time profiles in the two spectral domains
are not similar. The other two 17 GHz BPs are quiescent with
fluctuations superposed upon them. For the quiet region XBP, we believe
that the 17 GHz emission is thermal.
@--------------------------------------------------------------------
Title: The radio source around Eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Nelson, G. J.;
Drake, S. A.; Kundu, M. R.
Bibliographic Code: 1994ApJ...429..380W
Abstract
We present high spatial resolution radio observations of the peculiar
southern star Eta Carinae, made with the Australian Telescope. The
images, at 8 and 9 GHz with a resolution of 1.0 arcsec show a source of
dimension 10 arcsec and total flux of 0.7 Jy dominated by a strong
central peak. The radio emission is unpolarized and offers no support to
models which invoke degenerate stars or more exotic objects within the
core of Eta Car. In these data we find no evidence for more than one
energy source in the core with arcsecond separations as some infrared
observations have suggested. Several levels of structure are evident in
the radio image, which shows symmetry on the larger scales. Conventional
formulae for stellar wind radio sources give a mass loss rate of order 3
x 10-4 Solar Mass/yr based on the radio flux in the central
peak, which yields a wind momentum flux of order 20% of the momentum
flux available from the star's radiation field. The radio emission at
these frequencies is consistent with thermal emission from gas flowing
away from a 'luminous blue variable' star (LBV) Eta Car is probably the
brightest thermal stellar wind radio source in the sky.
@--------------------------------------------------------------------
Title: Solar cycle variation of the microwave spectrum and
total irradiance
Authors: Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1994SoPh..152..167S
Abstract
We have extended the proxy relationship between irradiance and
microwaves by using the daily solar fluxes from Toyokawa Observatory at
1000, 2000, 3750 and 9400 MHz in addition to the Ottawa 2800 MHz flux
for the years 1980-1989. It turns out that the flux at 1000 MHz is
better correlated with irradiance than the flux at higher frequencies --
an unexpected result. We have also found that the spectrum of the flux
shows shape changes that are related to the number and type of active
regions. Because of this the five-frequency spectral measurements of
microwave flux allow one to separate the sunspot and coronal features,
providing an improved proxy of solar variability.
@--------------------------------------------------------------------
Title: Nonthermal processes in flaring X-ray-bright points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; White, S. M.;
Hudson, H. S.; Harvey, K. L.; Kane, S. R.
Bibliographic Code: 1994ApJ...427L..59K
Abstract
X-ray-bright point (XBPs) are known to show variability on a number of
timescales, including impulsive X-ray brightenings. The relationship
between these XBP 'flares' and normal solar flares is poorly known. A
fundamental question is whether nonthermal acceleration of particles
takes place in XBP flares. We address this issue by searching for
nonthermal radio emission at metric wavelengths from flaring XBPs
identified in Yohkoh soft x-ray telescope (SXT) data. Unequivocal
evidence for type III-like radio bursts, usually attributed to beams of
nonthermal electrons on open field lines, is found. This suggests that
XBP flares are similar to normal flares and can indeed accelerate
nonthermal populations of energetic particles.
@--------------------------------------------------------------------
Title: Nonthermal radio emission associated with a coronal
disconnection event
Authors: Gopalswamy, N.; Kundu, M. R.; St. Cyr, O. C.
Bibliographic Code: 1994ApJ...424L.135G
Abstract
We have found possible radio signatures of a coronal disconnection event
observed by the Solar Maximum Mission Coronagraph/Polarimeter. The radio
emission seems to be produced by charged particles accelerated during
the same reconnection process which is responsible for the disconnection
event. We discuss the implications of the radio emission characteristics
to the reconnection process.
@--------------------------------------------------------------------
Title: Three dimensional coronal structures using Clark
Lake observations
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1994AdSpR..14...65S
Abstract
Throughout the quiet-Sun years 1982-1987, the Clark Lake Radioheliograph
mapped the solar corona on a daily basis at frequencies from 30 to 100
MHz. The Clark Lake maps show a variety of features which we have
analyzed quantitatively. Among the features are coronal streamers, which
appear to cross the solar disk during a solar rotation. We have modeled
the streamers with various geometries and density profiles, and computed
ray-tracing images for comparison with the Clark Lake Radio Observatory
(CLRO) maps. These models produce estimates of density and spatial
scales in 3 dimensions for the streamers. We discuss the significance of
these estimates and compare them with inferences made from optical
observations. One of the possible conclusions we draw from these
comparisons is that there are unresolved structures in streamers, not
observable optically in the limb data.
@--------------------------------------------------------------------
Title: Three-dimensional coronal structures using Clark
Lake observations
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1994SoPh..150..325S
Abstract
We have undertaken a study of coronal features observed at
meter-decameter wavelengths using the Clark Lake radioheliograph. Among
the coronal structures we have studied are the radio manifestations of
coronal streamers on the solar disk and above the solar limb. We have
analyzed the radio data quantitatively, using ray-tracing models for
comparison with the maps. Our study provides information about the
streamers' three-dimensional shapes, scales, and density profiles, for
comparison with related observations using white-light coronagraphs.
@--------------------------------------------------------------------
Title: Non-radial magnetic field structures in the solar
corona
Authors: Gopalswamy, N.; Kundu, M. R.; Raoult, A.; Pick, M.
Bibliographic Code: 1994SoPh..150..317G
Abstract
We report on the structure and geometry of coronal magnetic fields
inferred from the observations of meter-decimeter type 3 and moving type
4 radio bursts, associated with an H(alpha) flare. This is the first
report of type 3 radio bursts from the Nancay radioheliograph after it
acquired the two dimensional multifrequency capability. Dispersion of
the radio source positions with frequency suggests that open and closed
field lines are considerably inclined to the radial direction which is
consistent with the connectivity observed in the magnetogram. We suggest
that multiple arch systems are involved in the type 4 emission. From the
polarization and dispersion characteristics of the type 4 source, we
infer that the emission is due to fundamental plasma emission.
@--------------------------------------------------------------------
Title: Millimeter, microwave, hard X-ray, and soft X-ray
observations of energetic electron populations in
solar flares
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
Bibliographic Code: 1994ApJS...90..599K
Abstract
We present comparisons of multiwavelength data for a number of solar
flares observed during the major campaign of 1991 June. The different
wavelengths are diagnostics of energetic electrons in different energy
ranges: soft X-rays are produced by electrons with energies typically
below 10 keV, hard X-rays by electrons with energies in the range 10-200
keV, microwaves by electrons in the range 100 keV-1 MeV, and
millimeter-wavelength emission by electrons with energies of 0.5 MeV and
above. The flares in the 1991 June active period were remarkable in two
ways: all have very high turnover frequencies in their microwave
spectra, and very soft hard X-ray spectra. The sensitivity of the
microwave and millimeter data permit us to study the more energetic
(greater than 0.3 MeV) electrons even in small flares, where their
high-energy bremsstrahlung is too weak for present detectors. The
millimeter data show delays in the onset of emission with respect to the
emissions associated with lower energy electrons and differences in time
profiles, energy spectral indices incompatible with those implied by the
hard X-ray data, and a range of variability of the peak flux in the
impulsive phase when compared with the peak hard X-ray flux which is two
orders of magnitude larger than the corresponding variability in the
peak microwave flux. All these results suggest that the hard
X-ray-emitting electrons and those at higher energies which produce
millimeter emission must be regarded as separate populations. This has
implications for the well-known 'number problem' found previously when
comparing the numbers of non thermal electrons required to produce the
hard X-ray and radio emissions.
@--------------------------------------------------------------------
Title: Radio constraints on coronal models for dMe stars
Authors: White, S. M.; Lim, J.; Kundu, M. R.
Bibliographic Code: 1994ApJ...422..293W
Abstract
Radio data are used to test coronal models for dMe stars. Specifically,
we show that photospheric magnetic field observations imply that the low
corona of a dMe star should be saturated by magnetic fields with an
average strength in excess of 1 kG. In such fields the hot component of
the corona detected in X-ray observations (temperature of order 2 x
107 K) would be optically thick at least up to 15 GHz due to
thermal gyroresonance opacity. The resulting emission would easily be
detectable by radio observations and should have a radio spectrum rising
in the microwave range. We have carried out observations to test this
prediction, and in the majority of cases find that the observed fluxes
at 15 GHz are too low to be consistent with the assumptions. In the few
cases where the stars were detected at 15 GHz, the evidence indicates
that the observed emission is nonthermal. These results imply that the
hot component of the X-ray-emitting plasma in the corona is not
coincident with the strong magnetic fields in the lower corona. Because
the hot plasma must still be confined by closed magnetic field lines, it
is likely to be restricted to heights of the order of a stellar radius
above the photosphere. The results seem to imply a different genesis for
the two components of the X-ray-emitting corona of flare stars: the hot
component may be cooling flare plasma, while the cooler component
(temperature of order 3 x 106 K) is associated with a more
conventional coronal heating mechanism.
@--------------------------------------------------------------------
Title: Observing stellar coronae with the Goddard High
Resolution Spectrograph. 1: The dMe star AU
microscopoii
Authors: Maran, S. P.; Robinson, R. D.; Shore, S. N.;
Brosius, J. W.; Carpenter, K. G.; Woodgate, B. E.;
Linsky, J. L.; Brown, A.; Byrne, P. B.; Kundu, M. R.;
White, S.; Brandt, J. C.; Shine, R. A.;
Walter, F. M.
Bibliographic Code: 1994ApJ...421..800M
Abstract
We report on an observation of AU Mic taken with the Goddard High
Resolution Spectrograph (GHRS) aboard the Hubble Space Telescope. The
data consist of a rapid sequence of spectra covering the wavelength
range 1345-1375 A with a spectral resolution of 10,000. The observations
were originally intended to search for spectral variations during
flares. No flares were detected during the 3.5 hr of monitoring. A
method of reducing the noise while combining the individual spectra in
the time series is described which resulted in the elimination of half
of the noise while rejecting only a small fraction of the stellar
signal. The resultant spectrum was of sufficient quality to allow the
detection of emission lines with an integrated flux of 10-15
ergs/sq cm(sec) or greater. Lines of C I, O I, O V, Cl I, and Fe XXI
were detected. This is the first indisputable detection of the 1354 A Fe
XXI line, formed at T approximately = 107 K, on a star other
than the Sun. The line was well resolved and displayed no significant
bulk motions or profile asymmetry. From the upper limit on the observed
line width, we derive an upper limit of 38 km/s for the turbulent
velocity in the 107 K plasma. An upper limit is derived for
the flux of the 1349 A Fe XII line, formed at T approximately = 1.3 x
106 K. These data are combined with contemporaneous GHRS and
International Ultraviolet Explorer (IUE) data to derive the volume
emission measure distribution of AU Mic over the temperature range
104-107 K. Models of coronal loops in hydrostatic
equilibrium are consistent with the observed volume emission measures of
the coronal lines. The fraction of the stellar surface covered by the
footprints of the loops depends upon the loop length and is less than
14% for lengths smaller than the stellar radius. From the upper limit to
the estimated width of the Fe XXI line profile we find that the we
cannot rule out Alfven wave dissipation as a possible contributor to the
required quiescent loop heating rate.
@--------------------------------------------------------------------
Title: The effects of large- and small-scale density
structures on the radio from coronal streamers
Authors: Thejappa, G.; Kundu, M. R.
Bibliographic Code: 1994SoPh..149...31T
Abstract
The radio observations of the coronal streamers obtained using Clark
Lake radioheliograph at 73.8, 50.0, and 38.5 MHz during a period of
minimum activity in September 1986 are presented. Streamers appear to
correlate with two prominent disk sources whose intensites fluctuated
randomly. The variations in half-power diameter of the radio Sun are
found to correspond with the variations in the white-light extents of
the coronal streamers. It appears that the shape of the radio Sun is not
a function of the phase of the solar cycle; instead it depends on the
relative positions of the streamers in the corona. The observed peak
brightness temperatures, TB, of the streamers are found to be
very low, being approximately equal to 6 x 104 K. We compute
the brightness temperature distribution along the equator by tracing the
rays in the coronal plasma. The rays are deflected away by the streamers
before reaching the critical density level, whereas they penetrate
deeper into the coronal hole for small angles between the line of sight
and the streamer axis. As a consequence, it is found that the streamers
and coronal holes appear in the calculated equatorial brightness
distribution as irregular brightness depressions and enhancements,
respectively. The fine structures are found to disappear when the
scattering due to small-scale density inhomogeneities is included in the
ray-tracing calculations. The required relative level of density
fluctuations, epsilon1 = (delta N)/N, is found to be greater
than 12% to reduce the peak brightness temperature from 106 K
to 6 x 104 K for all the three frequencies.
@--------------------------------------------------------------------
Title: Observations of the 1991 Eclipse at 3.5 MM
Wavelength
Authors: White, S. M.; Kundu, M. R.
Bibliographic Code: 1994IAUS..154..167W
Abstract
@--------------------------------------------------------------------
Title: Interferometry of Solar Flares at 3-mm Wavelength
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
Bibliographic Code: 1994IAUS..154..131K
Abstract
@--------------------------------------------------------------------
Title: A Search for gamma-Ray Emission from Active Stars
Authors: White, S. M.; Harmon, B. A.; Lim, J.; Kundu, M. R.
Bibliographic Code: 1994ASPC...64..498W
Abstract
@--------------------------------------------------------------------
Title: Variability in Sunspot Associated Microwave
Emission: Umbral Oscillations?
Authors: Gopalswamy, N.; Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1993AAS...183.6808G
Abstract
We report on microwave observations of sunspot associated emission that
shows variability over a time scale of minutes. To our knowledge, this
is the first time such rapid variability has been observed in microwave
radiation from a sunspot. These observations were obtained by the Very
Large Array (VLA) on April 24, 1992 at 2cm. The radio emission from the
sunspot umbra was in the form of several compact sources with a size
less than 4 arcsec. The time evolution of the peak flux of these sources
showed significant time variations which were sometimes periodic. The
period of these ocillations was approximately 3 min, similar to that of
intensity and Doppler shift oscillations observed in optically thin,
transition region lines such as C IV (1548.19 Angstroms) in sunspot
umbrae. There were also morphological changes in the extended sunspot
emission over which the compact sources were superposed. We also
observed the appearance of new compact sources within the umbra where
there was reduced emission before. The brightness temperatures of these
compact sources were in the range (1-5)times 10(5) K. We explore
possible interpretations of the time variability.
@--------------------------------------------------------------------
Title: Evolution of a Solar Active Region and Flare
Productivity
Authors: Kundu, M. R.; Shibasaki, K.; Enome, S.; Nitta, N.;
Bruner, M.
Bibliographic Code: 1993AAS...183.6807K
Abstract
We have studied the evolution of an active region (AR 7515) in terms of
flare productivity. This region appeared on the east limb on May 23,
1993 and continued its onward march across the disk. We followed its
evolution until June 2. This region produced many small flares. We
studied the topology, both magnetic and structural of the flaring region
as observed at 17 GHz by the Nobeyama radio Heliograph (NRH) with a
spatial resolution of 10 arcsec and the Yohkoh SXT which has a spatial
resolution of 2.5 arcsec. Among other things, we find: (i) Frequently a
flare starts with the appearance of a new region/loop which interacts
with a pre-existing loop; this interaction acta as a flare trigger. (ii)
There appear to exist multiple sets of interacting loops in the same
active region. Different bursts on the same day seem to come from
diffrent sets of interacting loops. (iii) Sometimes two or more sets of
interacting loops can activate at the same time, giving rise to
different peaks in the same burst. In the decay phase of some bursts
there may appear a new or reactivated region/loop which becomes the
source of new burst emission. (iv) A simple spiky burst in general
originates from a narrow region and by implication from a compact set of
interacting loops.
@--------------------------------------------------------------------
Title: VLA Observations of a High Coronal Flare
Authors: Raulin, J. P.; Gopalswamy, N.; Kundu, M. R.;
Nitta, N.
Bibliographic Code: 1993AAS...183.0706R
Abstract
We present radio observations of a coronal flare which occurrred on 1993
April 22, in a weak magnetic field region to the west of AR 7477. The
observations were made by the Very Large Array (VLA) at 20 and 90 cm.
The event consists of bright (brightness temperature of 10(10) K)
unpolarized bursts, followed by a longlasting unpolarized continuum with
moderately high brightness temperature (2-3 10(9) K) in the high corona
(90 cm observations). The low coronal counterpart of this flare is a
weak and moderatly polarized 20 cm radio emission. Full disk Yohkoh
images show that the corresponding radio emission is located in or above
magnetic loops connecting AR 7477 and its neighborhood. The presence of
permanent and non-varying noise storm associated with AR 7477 seems to
indicate that the overall magnetic field structure of the active region
is unaffected by the flare. The coronal radio source which is indicative
of acceleration of electrons to nonthermal energies, is not associated
with major Halpha emissio n nor with bright X ray emission. The
absence of any detectable circular polarization, as well as the high
brightness temperature, seems to indicate that the 90 cm emission is
second harmonic plasma emission.
@--------------------------------------------------------------------
Title: Evidence for Ordinary Mode Emission from Microwave
Bursts
Authors: Alissandrakis, C. E.; Nindos, A.; Kundu, M. R.
Bibliographic Code: 1993SoPh..147..343A
Abstract
We analyze high-resolution, one-dimensional observations of simple
microwave bursts, obtained at 4.9 GHz with the Westerbork Synthesis
Radio Telescope in 1980, together with Halpha photographs of the
associated flares from the Observatories of Athens and Meudon. In most
cases the polarization structure can be interpreted in terms of
extraordinary mode emission, taking into account the polarity of the
underlying magnetic field and propagation effects, which may lead to
inversion of the sense of polarization in the limbward part of the
flaring loop. We found evidence for ordinary mode emission in two
classes of events. In one class theo-mode comes from regions overlying
strong magnetic field, which we interpret in terms of thermal
gyroresonance absorption of the extraordinary mode at the third harmonic
of the gyrofrequency. In the other class the entire burst emits in
theo-mode, which may be attributed to high gyrosynchrotron optical
depth.
@--------------------------------------------------------------------
Title: Structure of a fast coronal mass ejection from radio
observations.
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1993AdSpR..13R..75G
Abstract
The authors investigate the thermal structure of a coronal mass ejection
(CME) in meter-dekameter wavelengths and compare it with the optical
evidence. The multifrequency observations enable us to infer the three
dimensional structure of the CME. The authors estimated the mass of the
CME and found to be in reasonable agreement with the range of values
obtained from white light observations.
@--------------------------------------------------------------------
Title: Interferometric observations of solar flares at 3 mm
wavelength
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
Bibliographic Code: 1993AdSpR..13..289K
Abstract
We report on the observations of a number of flares at a wavelength of
3.5 mm during the 1991 June solar campaign. Many flares, including small
ones, show an impulsive phase at milllimeter wavelengths which indicates
the presence of MeV electrons, and the millimeter observations are far
more sensitive to such electrons than are current gamma-ray detectors.
However, these energetic electrons do not always show a good correlation
with the lower-energy electrons which produce hard X-rays below 100 keV.
The production efficiency of MeV electrons seems to vary considerably
from flare to flare. An extended phase similar to the soft X-ray
behaviour is also seen at millimeter wavelengths, which we attribute to
dense hot material radiating thermal bremsstrahlung. In the impulsive
onset the millimeter emission seems to be consistently delayed with
respect to the hard X-rays.
@--------------------------------------------------------------------
Title: A Study of the Solar Active Regions Using
Simultaneous VLA and Yohkoh Soft X-ray Imaging:
CoMStOC `92
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.;
Lemen, J. R.; Strong, K. T.; Schmelz, J. T.
Bibliographic Code: 1993BAAS...25R1213G
Abstract
@--------------------------------------------------------------------
Title: Millimeter, Microwave and X-Ray Morphology and
Spectra of the 07Jan92 Flare
Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.;
Kundu, M. R.; Gary, D. E.; Hudson, H. S.
Bibliographic Code: 1993BAAS...25Q1223S
Abstract
@--------------------------------------------------------------------
Title: Hard X-ray and Radio Spectra for Solar Flares from
AR 6659
Authors: White, S. M.; Murphy, R.; Schwartz, R. A.;
Kundu, M. R.; Gopalswamy, N.; Lim, J.
Bibliographic Code: 1993BAAS...25Q1222W
Abstract
@--------------------------------------------------------------------
Title: Solar Coronal Plasma and Magnetic Field Diagnostics
Using SERTS and Coordinated VLA Observations
Authors: Brosius, J. W.; Davila, J. M.; Thompson, W. T.;
Thomas, R. J.; Holman, G. D.; Gopalswamy, N.;
White, S. M.; Kundu, M. R.; Jones, H. P.
Bibliographic Code: 1993BAAS...25.1224B
Abstract
@--------------------------------------------------------------------
Title: VLA, OVRO, Yohkoh and Optical Observations During
CoMStOC
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.;
Lemen, J.; Strong, K. T.; de La Beaujardiere, J.
Bibliographic Code: 1993BAAS...25.1213S
Abstract
@--------------------------------------------------------------------
Title: VLA and Yohkoh Observations of an M1.5 Flare
Authors: Gopalswamy, N.; Kundu, M. R.; Lemen, J. R.;
Nitta, N.; Strong, K. T.
Bibliographic Code: 1993BAAS...25.1186G
Abstract
@--------------------------------------------------------------------
Title: A Multiwavelength Portrait of a Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1993BAAS...25.1183W
Abstract
@--------------------------------------------------------------------
Title: Meter-Wave Radio Emission from Flaring X-ray Bright
Points
Authors: Kundu, M. R.; Strong, K. T.; Pick, M.; Kane, S. R.;
Harvey, K.; White, S. M.
Bibliographic Code: 1993BAAS...25.1180K
Abstract
@--------------------------------------------------------------------
Title: The Radio Source Around eta Carinae
Authors: White, S. M.; Duncan, R. A.; Lim, J.; Nelson, G. J.;
Drake, S. A.; Kundu, M. R.
Bibliographic Code: 1993AAS...182.3906W
Abstract
The first high--spatial--resolution (1{('') }) radio image of the source
surrounding the famous massive southern star eta Carinae has been
obtained with the Australia Telescope. The image shows a number of
interesting features: a strong central peak; ridges of emission close to
the peak and extending away from it in the directions of putative
``jets'' seen in the HST image of the region, and also other ridges in
the directions of the lobes of the Homunculus; a box--like extended
feature of dimension 7{('') } \ times 5{('') }, with its major axis
orthogonal to the major axis of the Homunculus; and two fainter lobes
extending to 5{('') } \ from the star in the directions of both lobes of
the Homunculus. The radio image bears a strong resemblance to the
high--resolution infra--red images of the region around the star. No
radio emission associated with the more extended X-ray--emitting nebula
is detected. The current rate of mass loss from the star is estimated,
and physical conditions within the nebula are discussed.
@--------------------------------------------------------------------
Title: Spectral observations of active region sources with
RATAN-600 and WSRT
Authors: Alissandrakis, C. E.; Gel'Frejkh, G. B.;
Borovik, V. N.; Korzhavin, A. N.; Bogod, V. M.;
Nindos, A.; Kundu, M. R.
Bibliographic Code: 1993A&A...270..509A
Abstract
We present spectral observations of neutral line and sunspot associated
sources obtained with the RATAN-600 radio telescope and the WSRT in the
wavelength range of 2 to 6 cm. Sources associated with large sunspots
have flat spectra, while neutral line sources have very steep spectra.
In the case of a large spot we estimated the magnetic field to be at
least 2700 G at the base of the transition region and 1800 G in the low
corona. We consider possible interpretations of the radio emission above
the neutral lines. Gyroresonance emission at the fourth harmonic is
inadequate, whereas emission from a small population of nonthermal
electrons (total number 10 exp 30 to 10 exp 31) with a delta = 3 power
law distribution seems to be sufficient.
@--------------------------------------------------------------------
Title: Thermal and nonthermal emissions during a coronal
mass ejection
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1993SoPh..143..327G
Abstract
Observations were made of thermal and nonthermal radio emissions from a
coronal mass ejection (CME) at meter-decameter wavelengths. The speed of
the CME was found to be approximately 450 km/sec. It was possible to
observe the thermal structure of the CME in radio due to the absence of
nonthermal radio emission in the beginning of the event, and the
weakness of the following event. Several minutes after the onset of the
CME, type III bursts and a nonthermal continuum began. Radio and optical
observations are used to show that the CME was not driven by the flare.
The thermal structure and geometry of the mass ejection in radio is
investigated and compared with the optical evidence. Lastly, a schematic
model of the event is developed to show that particle acceleration high
in the corona is possible.
@--------------------------------------------------------------------
Title: A 1.5 GHz radio survey of the Hyades open stellar
cluster
Authors: White, S. M.; Jackson, P. D.; Kundu, M. R.
Bibliographic Code: 1993AJ....105..563W
Abstract
Results of a radio survey of the Hyades open stellar cluster carried out
with the VLA at 1.5 GHz are reported. Seventeen fields containing over
150 cataloged stars were mapped down to a limiting sensitivity ranging
from 0.3 mJy at the centers of the fields to 0.9 mJy at a distance of 20
arcmin from field centers. Two stars were detected as radio sources: the
evolved spectroscopic binary V471 Tau, consisting of a white dwarf and a
red dwarf; and the apparently premain-sequence G+K star spectroscopic
binary HD 27130. The failure to detect any single stars as radio sources
is generally consistent with the age-rotation-activity paradigm,
according to which stellar activity is due to magnetic fields produced
by dynamo action in rapidly rotating stars and should decrease with age
as a star spins down due to magnetic braking. It is concluded that the
Hyades M dwarf population is not more active at radio wavelengths than
the nearby flare star population, or else the number of flare stars in
the Hyades is much less than presently assumed.
@--------------------------------------------------------------------
Title: Analysis of EUV, Microwave and Magnetic Field
Observations of Solar Plage
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.;
Thompson, W. T.; Thomas, R. J.; Holman, G. D.;
White, S. W.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1993ASPC...46..291B
Abstract
@--------------------------------------------------------------------
Title: Solar observations with a millimeter-wavelength
array
Authors: White, S. M.; Kundu, M. R.
Bibliographic Code: 1992SoPh..141..347W
Abstract
An introduction to the field of solar millimeter interferometry is
given. Solar observations using the BIMA at Hat Creek since 1989 are
reviewed along with other solar millimeter observations. The radiation
mechanisms relevant to solar millimeter astronomy are discussed, and
observations in the millimeter and microwave ranges are compared. The
use of closure phases in arrays containing a small number of elements is
examined.
@--------------------------------------------------------------------
Title: The high-frequency characteristics of solar radio
bursts
Authors: Lim, J.; White, S. M.; Kundu, M. R.; Gary, D. E.
Bibliographic Code: 1992SoPh..140..343L
Abstract
The millimeter, microwave, and soft X-ray emission from a number of
solar flares is compared in order to determine the properties of the HF
radio emission of flares. The millimeter observations use a sensitive
interferometer at 86 GHz which offers much better sensitivity and
spatial resolution than most previous high-frequency observations. The
86-GHz emission onset appears often to be delayed with respect to the
microwave onset. Even in large flares the millimeter-wavelength emission
can arise in sources of only a few arc sec dimension. The millimeter
emission in the impulsive phase does not correlate with the soft X-ray
emission, and thus is unlikely to contain any significant thermal
bremsstrahlung component. The electron energy distributions implied by
the millimeter observations are much flatter (spectral indices of 2.5 to
3.6) than is usual for microwave or hard X-ray observations.
@--------------------------------------------------------------------
Title: Are coronal type II shocks piston driven?
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1992AIPC..264..257G
Abstract
Flare blast waves and shocks piston driven by coronal mass ejections
(CMEs) have been proposed to be responsible for generating type II radio
bursts in the solar corona. The idea for piston-driven shocks came
primarily from temporal association of shocks and CMEs. Our compilation
of CME events with simultaneous radio observations with positional
information supports idea of flare blast waves.
@--------------------------------------------------------------------
Title: Unusually low coronal radio emission at the solar
minimum
Authors: Thejappa, G.; Kundu, M. R.
Bibliographic Code: 1992SoPh..140...19T
Abstract
The paper reports 2D observations of the quiet sun at 73.8, 50.0, and
38.5 MHz obtained with the Clark Lake Radioheliograph during the sunspot
minimum period of September 1986. The observed peak brightness
temperatures during the entire period of sunspot minimum are found to be
extremely low, lying in the range (0.6-2.5 x 10 exp 5 K). It is shown
that these low values cannot be explained by the generally adopted
models for Ne and Te in a homogeneous corona. The effect of scattering
by random density fluctuations is introduced in order to decrease the
values of predicted Tb. The value of peak Tb is computed as a function
of relative rms density fluctuations, and the fluctuations should be in
the range from 0.07 to 0.19, 0.1 to 0.25, and 0.15 to 0.35,
respectively, at 38.5, 50.0, and 73.8 MHz, respectively, to explain the
observed low brightness temperatures.
@--------------------------------------------------------------------
Title: Radio flares and magnetic fields on weak-line T
Tauri stars
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
Bibliographic Code: 1992A&A...259..149W
Abstract
We report the first detection of circular polarization in the radio
emission of two weak-line T Tauri stars. This is direct confirmation of
the presence of magnetic fields in the coronae of these stars. The
degree of polarization at 5 GHz is small, consistent with previous
observations which did not find measurable polarization. We have also
observed a radio flare on one of the two stars. The rising spectrum of
the radio emission together with the low degree of polarization are
strong evidence that radio outbursts on this class of stars are due to
nonthermal gyrosynchrotron emission which is optically thick in the
microwave range. One of the two stars shows no evidence for
circumstellar material, and thus can be classified as 'naked'. However
the other apparently has a dust disk, and the evidence of flaring on
this star indicates that the mechanism involved does not require an
empty circumstellar environment.
@--------------------------------------------------------------------
Title: Estimation of the mass of a coronal mass ejection
from radio observations
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1992ApJ...390L..37G
Abstract
The mass of a coronal mass ejection (CME) is estimated using
meter-decametric observations obtained with the Clark Lake
multifrequency radioheliograph. Mass estimates in the past were made
using coronagraph and white-light photometer observations. Since the
radiation at radio and optical wavelength regimes has different physical
origins, the radio method can provide an independent check on the mass
estimates. The estimate of the 1986 February 16 CME using the radio
method is close to the average value of CME masses reported in the
literature.
@--------------------------------------------------------------------
Title: The Structure of the Corona of dMe Flare Stars
Authors: White, S. M.; Lim, J.; Kundu, M. R.
Bibliographic Code: 1992AAS...180.6005W
Abstract
There is now considerable information on both the surface magnetic
fields of dMe flare stars and on the thermal (X-ray emitting)
populations in their coronae. We show that the simplest picture of the
corona of a dMe flare star based on the measured photospheric magnetic
field strengths, the measured filling factors of these fields, and the
X-ray emission from their coronae, are inconsistent with radio
observations of the coronae. We discuss possible resolutions of this
dilemma.
@--------------------------------------------------------------------
Title: Millimeter Observations of Solar Flares
Authors: Silva, A. V.; Lin, R. P.; de Pater, I.; White, S. M.;
Kundu, M. R.
Bibliographic Code: 1992AAS...180.4510S
Abstract
@--------------------------------------------------------------------
Title: Simultaneous Hard X-ray, Soft X-ray, Millimeter and
Microwave Observations of a Solar Flare
Authors: White, S. M.; Kundu, M. R.; Lim, J.; Gopalswamy, N.
Bibliographic Code: 1992AAS...180.4504W
Abstract
We present non-imaging data across a wide range of wavelengths for a
solar flare which occurred on 1991 June 13. This flare is of interest
because it shows a spike in hard X-rays at the beginning of the event
which had a relatively hard X-ray spectrum, and was followed by a much
softer impulsive phase. We present the BATSE and OSSE observations (from
the Gamma Ray Observatory): the former have good time resolution, while
the latter provide well-resolved spectral information. These are
contrasted with the GOES soft-X-ray data on the hot thermal component in
the corona, and radio observations up to 86 GHz which are sensitive to
both the nonthermal and thermal components of the flare. The 86 GHz data
from the BIMA millimeter interferometer show a spike in the impulsive
phase coincident with the hard X-ray spike above 100 keV, as well as a
long-duration thermal phase which appears to be consistent with an
origin in the same material seen by GOES. We discuss the implications of
the observations for particle acceleration in this flare.
@--------------------------------------------------------------------
Title: Analysis of EUV, Microwave, and Magnetic Field
Observations of a Solar Active Region
Authors: Brosius, J. W.; Davila, J. M.; Jones, H. P.;
Thompson, W. T.; White, S. M.; Gopalswamy, N.;
Kundu, M. R.
Bibliographic Code: 1992AAS...180.4002B
Abstract
@--------------------------------------------------------------------
Title: Radio Observations During the 1991 June Campaign of
Max'91 in Conjunction with Compton GRO Experiments
Authors: Kundu, M. R.
Bibliographic Code: 1992AAS...180.3403K
Abstract
A summary of all available radio observations made during the 1991 June
campaign of the MAX '91/Flare 22 program will be presented. The
presentation will be concerned primarily with millimeter wavelength
(BIMA and Nobeyama) and centimeter wavelengths (Owens Valley and
Nobeyama) observations. Emphasis will be given to the question of
millimeter observations as a diagnostic for Mev electrons in solar
flares (gamma ray flares --- BATSE and OSSE data), millimeter emission
occurring at the steep rise phase of hard X-ray emitting electrons
(BATSE data) and delay of millimeter emission onset and 25-100 Kev
X-rays (BATSE data). Implications of these results for generation of
millimeter emission and particle acceleration process will be discussed.
The Nobeyama data consist of non-imaging patrol observations at several
frequencies in the frequency range 1--80 GHz, and Owens Valley data were
obtained using the frequency agile interferometer in the frequency range
1--18 GHz. Light curves and spectral information of the most energetic
flares will be presented.
@--------------------------------------------------------------------
Title: 2-cm Observations of Quiescent and Flaring Emission
from a Solar Active Region
Authors: Lim, J.; White, S. M.; Kundu, M. R.
Bibliographic Code: 1992AAS...180.1102L
Abstract
We present 2-cm images of a solar active region comprising a large
leading spot and several smaller trailing spots, observed with the VLA
on 1989 Dec 14 and 16. On both days, slowly-varying quiescent emission
and impulsive flaring emission were detected. Comparisons of the radio
images with white-light pictures and magnetograms obtained on Dec 13 and
17 revealed that the quiescent emission originated almost entirely from
above the penumbra of large spots, whereas the flaring emission
originated from regions of complex magnetic field topology near but not
necessarily above magnetic neutral lines. The most intense source of
quiescent emission had a relatively low brightness-temperature ( ~ 10(5)
K), was highly circularly polarized (ranging from about 30\ trailing
edge (i.e., limbward side) of the large leading spot. We discuss models
for this emission, constrained by the low brightness temperature but
high polarization. The weaker flare of Dec 14 showed a single resolved
source, and was weakly circularly-polarized. The stronger flare of Dec
16 comprised a strong source with multiple peaks and several weaker
compact sources, all with low degrees of circular polarization. Snapshot
images of this flare showed an elongated feature moving rapidly away
from the main region of emission and joining with the compact sources.
We discuss likely mechanisms for this feature, and emission process(es)
responsible for the flares.
@--------------------------------------------------------------------
Title: A 5 GHz radio survey of selected POST T Tauri and
naked T Tauri stars
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
Bibliographic Code: 1992A&A...257..557W
Abstract
Results of a radio survey of weak-lined T Tauri (variably classified as
either post T Tauri or naked T Tauri) stars at 5 GHz are reported.
Thirty-two targets, chosen on the basis of known high-activity levels or
youth indications, were observed, and 15, including eight previously
unknown radio sources, were detected. It is suggested that most
weak-lined T Tauris with high activity levels, e.g., as indicated by a
high X-ray flux, are likely to be detectable radio sources at some time,
but the radio emission goes through high and low phases. For the
subsample of 14 stars observed in Taurus-Auriga which were thoroughly
studied at IR, optical, and X-ray wavelengths, a clear association is
found between radio activity and youth.
@--------------------------------------------------------------------
Title: Observations of mode coupling in the solar corona
and bipolar noise storms
Authors: White, S. M.; Thejappa, G.; Kundu, M. R.
Bibliographic Code: 1992SoPh..138..163W
Abstract
High-spatial-resolution observations of the sun which reflect on the
role of mode coupling in the solar corona, and a number of new
observations are presented. It is shown that typically, polarization
inversion is seen at 5 GHz in active region sources near the solar limb,
but not at 1.5 GHz. Although this is apparently in contradiction to the
simplest form of mode coupling theory, it remains consistent with
current models for the active region emission. Microwave bursts show no
strong evidence for polarization inversion. Bipolar noise storm
continuum emission is discussed in some detail, utilizing recent VLA
observations at 327 MHz. It is shown that bipolar sources are common at
327 MHz. Further, the trailing component of the bipole is frequently
stronger than the leading component, in apparent conflict with the
'leading-spot' hypothesis. The observations indicate that, at 327 MHz,
mode coupling is apparently strong at all mode-coupling layers in the
solar corona. The 327 MHz observations require a much weaker magnetic
field strength in the solar corona to explain this result than did
earlier lower-frequency observations: maximum fields are 0.2 G. This is
a much weaker field than is consistent with current coronal models.
@--------------------------------------------------------------------
Title: Millimeter and hard X ray/gamma ray observations of
solar flares during the June 1991 GRO campaign
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.; Lim, J.
Bibliographic Code: 1992NASCP3137..502K
Abstract
We have carried out high-spatial-resolution millimeter observations of
solar flares using the Berkeley-Illinois-Maryland Array (BIMA). At the
present time, BIMA consists of only three elements, which is not
adequate for mapping highly variable solar phenomena, but is excellent
for studies of the temporal structure of flares at millimeter
wavelengths at several different spatial scales. We present BIMA
observations made during the Gamma Ray Observatories (GRO)/Solar Max
1991 campaign in Jun. 1991 when solar activity was unusually high. Our
observations covered the period 8-9 Jun. 1991; this period overlapped
the period 4-15 Jun. when the Compton Telescope made the Sun a target of
opportunity because of the high level of solar activity.
@--------------------------------------------------------------------
Title: High dynamic range multifrequency radio observations
of a solar active region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1992ApJS...78..599W
Abstract
High-dynamic-range multifrequency radio observations of a solar active
region are presented. The evolution of the region is followed at 5 GHz
as it rotates from the limb to disk center, and when it is at disk
center, observations at 0.33, 1.5, 5, 8.4, and 15 GHz are used to
analyze the distribution of density and magnetic field within the active
region. A dynamic range of up to 1500 (at 8.4 GHz) was achieved because
these data were well suited to the self-calibration technique. The
signatures of both optically thick gyroresonance emission are
unambiguously identified, and magnetic fields and optically thin thermal
free-free emission are outlined. Images are compared at 5 and 8.4 GHz in
order to identify regions in the trailing part of the active region
where optically thin four-harmonic gyroresonance emission is
contributing to the observed brightness temperatures at 5 GHz,
indicating the presence of 450 G fields.
@--------------------------------------------------------------------
Title: Multifrequency observations of a remarkable solar
radio burst
Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.;
Gary, D. E.; Hurford, G. J.; Kucera, T.;
Bieging, J. H.
Bibliographic Code: 1992ApJ...384..656W
Abstract
Observations of an impulsive solar-radio burst from three observatories
are presented. The striking observational aspects of this flare are that
the time profile was identical throughout at 8.6, 15, and 86 GHz, that
the spectrum was apparently flat from 15 to 86 GHz, and that there was a
sharp cutoff in the spectrum between 5.0 and 8.6 GHz. The simplest
interpretation of the cutoff, namely as a plasma frequency effect, leads
to the conclusion that there was exceptionally high-density material in
the solar corona (of about 5 x 10 exp 11/cu cm). Very Large Array images
at 15 GHz show a single-loop structure which brightened uniformly and
showed little change in size during the whole impulsive phase. The flat
spectrum is consistent with optically thin thermal bremsstrahlung
emission, but the lack of observed soft X-ray emission and other
properties of the flare cannot easily be accommodated by this mechanism.
The possibility is explored that the emission is optically thick due to
thermal absorption of nonthermal gyrosynchrotron emission, or optically
thin gyrosynchrotron emission absorbed by high-density material
intervening along the line of sight. Both of these explanations also
face difficulties.
@--------------------------------------------------------------------
Title: Radio observations of weak-lined T Tauri stars
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
Bibliographic Code: 1992MmSAI..63..751W
Abstract
We report the results of a search for radio-continuum emission from
weak-lined T Tauri stars selected on the basis of a range of criteria. A
correlation is found with strong X-ray emission and with youth. All the
stars in the survey older than about 20 million years were not detected
as radio sources. A flare was seen on one of the survey targets, with a
rise time of several hours. Circular polarization was also seen in two
of the targets, providing the first direct confirmation of the presence
of magnetic fields on these stars.
@--------------------------------------------------------------------
Title: Radio observations of solar and stellar coronae
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 1992MmSAI..63..715K
Abstract
Recent results of radio observations of the solar and stellar coronae
are reviewed. Attention is given to the results obtained on quiet-sun
fine structures; the active region observations, with particular
consideration given to the soft X-ray and radio comparisons of
observations made during the Coronal Magnetic Structures Observing
Campaign and the strength of the magnetic fields in the corona; the
radio observations of solar flares; and the radio observations of
stellar coronae of the RS Canum Venaticorum binaries, M dwarf stars,
pre-main-sequence stars, and chemically-peculiar B stars. Also discussed
are current issues in stellar radiophysics and perspectives in solar
radio physics.
@--------------------------------------------------------------------
Title: Meter-decameter radio emission associated with a
coronal mass ejection
Authors: Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1992LNP...399..268K
Abstract
A study of meter-dekameter radio emission associated with the 1986 Feb
10 coronal Mass ejection event is presented here. The event was
accompanied by a major flare (optical importance 1B and X-ray importance
C9.6), preceded by a filament disappearance. Changes in the intensity of
a pre-existing noise storm was observed during the onset of the flare. A
flare continuum, a moving type IV, and a type II occurred during the
event. The event was also associated with a strong hard X-ray burst. The
speeds of moving type IV burst and CME were of the same order of 1600
kms -1, while the type II shock speed was 1900 kms -1. The positional
data indicate that the moving type IV burst and the inferred type II
shock had different trajectories. The moving type IV burst was confined
to one leg of the CME while the type II shock was far ahead of the CME
leading edge. We discuss the inferred relation among different entities
such as the CME, type II shock, type IV plasmoid and the erupting
filament.
@--------------------------------------------------------------------
Title: Largescale Structures Associated with Eruptive
Flares and Radio Waves
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1992LNP...399..207G
Abstract
@--------------------------------------------------------------------
Title: A 5 GHz Survey of Weak-Lined T Tauri Stars
Authors: White, S. M.; Pallavicini, R.; Kundu, M. R.
Bibliographic Code: 1992ASPC...26..334W
Abstract
@--------------------------------------------------------------------
Title: HST Observations of the Flare Star AU MIC
Authors: Robinson, R. D.; Shore, S. N.; Carpenter, K. G.;
Woodgate, B. E.; Maran, S. P.; Brandt, J. C.;
Kundu, M. R.; White, S. M.; Linsky, J. L.;
Walter, F. M.
Bibliographic Code: 1992ASPC...26...31R
Abstract
@--------------------------------------------------------------------
Title: VLA observations of solar active regions at 6 and 20
CM
Authors: Alissandrakis, C. E.; Kundu, M. R.;
Shevgaonkar, K. R.
Bibliographic Code: 1991A&A...251..276A
Abstract
High-resolution observations are presented of two active regions at 6
and 20 cm over a period of 5 days, together with H-alpha and
photospheric magnetic fields. The large-scale emission at 20 cm is
associated with the H-alpha plage. In one region the strongest source
was over the neutral line, near the tip of an active-region filament,
which indicates that the emission probably originated in small-scale
coronal loops. In the second region the peak of the emission was near a
well-developed sunspot. Neither region showed evidence of large-scale
loops joining their preceding and following parts. Several other sources
were observed at 20 cm; a source associated with an H-alpha plage region
crossed by a filament and one associated with a small bipolar region are
briefly discussed. The 6-cm emission from a well-developed spot showed
clearly the characteristics expected from gyroresonance model
computations.
@--------------------------------------------------------------------
Title: Time Resolved Observations of the Lyman-Alpha Region
in AU Mic with the Goddard High Resolution
Spectrograph
Authors: Woodgate, B. E.; Maran, S. P.; Carpenter, K. G.;
Robinson, R. D.; Shore, S. N.; Linsky, J. L.;
Byrne, P. B.; Kundu, M. R.
Bibliographic Code: 1991BAAS...23.1383W
Abstract
@--------------------------------------------------------------------
Title: An Investigation of the Flare Star AU Mic with the
Goddard High Resolution Spectrograph on the Hubble
Space Telescope
Authors: Maran, S. P.; Woodgate, B. E.; Carpenter, K. G.;
Robinson, R. D.; Shore, S. N.; Linsky, J. L.;
Brown, A.; Byrne, P. B.; Kundu, M. R.; White, S.;
Brandt, J. C.; Shine, R. A.; Walter, F. M.
Bibliographic Code: 1991BAAS...23.1382M
Abstract
@--------------------------------------------------------------------
Title: Large-scale features of the sun at 20 centimeter
wavelength
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
Bibliographic Code: 1991ApJ...379..366G
Abstract
Results are reported from an experimental study of the characteristics
of large-scale coronal structures such as active regions, plages,
filaments, and coronal holes using data obtained with the VLA at 1.5 GHz
during the period September 11-17, 1988. The radio data were
supplemented with He 10830- A, H-alpha, and Calcium-K spectroheliograms.
A statistical analysis of some of the characteristics of the active
regions is performed. Most of the active region sources were found to be
about 100 arcsec in size, with bridges between regions common; lower
brightness temperature regions showed a higher degree of polarization in
general. The maximum polarization was found at the edge of active
regions but well within the associated plages. The degree of
polarization from bright active regions was small (not more than 20
percent), in agreement with previous results. Evidence was found for
compression of preexisting flux by the emerging flux from a new region,
which took place in the apparent absence of magnetic reconnection.
@--------------------------------------------------------------------
Title: VLA observations of interacting flaring loops
Authors: Kundu, M. R.; White, S. M.; McConnell, D. M.
Bibliographic Code: 1991SoPh..134..315K
Abstract
This study presents 4.9 GHz observations of an impulsive radio burst
observed at the VLA on May 16, 1981. The flare occurred in a complex
active region containing several spots. The radio burst lay at the edge
of an active-region microwave source, close to a neutral line. The
compact burst showed morphological evidence for the presence of two
loops in the rise phase, with the subsequent burst peak lying between
these loops. This suggests that interaction between the loops played
some role in the initiation of the flare. The flare spectrum is
consistent with thermal gyrosynchrotron emission. The main microwave
peak was displaced from the nearest H-alpha kernels by about 10 arcsec,
but there is strong evidence for post-flare loops coincident with the
H-alpha kernels during the later stages of the event.
@--------------------------------------------------------------------
Title: Coronal magnetic structures observing campaign. I -
Simultaneous microwave and soft X-ray observations
of active regions at the solar limb
Authors: Nitta, N.; White, S. M.; Kundu, M. R.;
Gopalswamy, N.; Holman, G. D.; Brosius, J. W.;
Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibliographic Code: 1991ApJ...374..374N
Abstract
Using simultaneous microwave and soft X-ray measurements made with the
Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator (XRP)
aboard the Solar Maximum Mission (SMM), we have studied two active
regions near the solar limb. These observations were taken as part of
the Coronal Magnetic Structures Observing Campaign (CoMStOC), a
collaboration designed to study the magnetic field in the solar corona.
The images in soft X-rays and at 20 cm wavelength are similar: both show
peaks above the active regions and extended bridge of emission 200,000
km long connecting the two regions. The brightness temperature of the 20
cm emission is lower than that predicted from the X-ray emitting
material, however; it can be attributed to free-free emission in cooler
(<106 K) plasma not visible to XRP, with an optical depth
˜1. The 6 cm emission is concentrated at lower altitudes and in a
˜160,000 km long bundle of loops in the northern active region.
Comparison of the 6 cm map with the potential magnetic field lines
computed from photospheric magnetic fields (measured 2 days earlier)
indicates that the 6 cm emission is associated with fields of less than
˜200 G. Such fields would be too weak to attribute the observed 6
cm emission to gyroresonance radiation. Analysis of the 6 cm loop bundle
indicates that it is strongly asymmetric, with the magnetic field in the
northern leg ˜2 times stronger than in the southern leg; the 6 cm
emission most likely arises from a combination of hot ( >= 2 ×
106 K) and cool plasmas, while the 20 cm emission becomes
optically thick in the cooler (˜9 × 103 K)
plasma. We estimate an Alfvén speed ˜7000 km s-1
and ratio of electron gyrofrequency to plasma frequency ˜1.0 in
the northern leg of the 6 cm loop.
@--------------------------------------------------------------------
Title: New observations of solar noise storm radiation at
decameter wavelengths
Authors: Thejappa, G.; Kundu, M. R.
Bibliographic Code: 1991SoPh..132..155T
Abstract
Multifrequency observations of storm continuum and other radio bursts
are presented. Based on their positional study and their correlation
with other coronal and photospheric features, the storm source is
located in the magnetic field lines lying above a single bipolar active
region. Energetic electrons trapped in the magnetic structures above the
spots must be responsible for the storm radiation. Spontaneous emission
of Langmuir waves by anisotropic distributions can explain both storm
continumm and bursts self-consistently.
@--------------------------------------------------------------------
Title: On the reconciliation of simultaneous microwave
imaging and hard X-ray observations of a solar flare
Authors: Nitta, N.; White, S. M.; Schmahl, E. J.;
Kundu, M. R.
Bibliographic Code: 1991SoPh..132..125N
Abstract
Microwave imaging data for a small flare with simultaneous hard X-ray
spectral observations are compared. The X-ray data suggest that the
power-law index delta of the energy distribution of the radiating
electrons is 5.3 (thick-target) which differs significantly from the
estimate (delta = 1.4) from a homogeneous optically-thin gyrosynchrotron
model which fits the radio observations well. In order to reconcile
these results, a double power-law energy spectrum is investigated for
the energetic electrons in the flare, as assumed by other authors: the
power law is steep at low energies and much flatter at the higher
energies which produce the bulk of the microwaves. The emission of soft
photons by the flat tail strongly contributes to the observed hard X-ray
range and would flatten the spectrum there. A thin-target model for the
X-ray emission is also inconsistent with radio data. An inhomogenous
gyrosychrotron model with a number of free parameters and containing an
electron distribution given by the thick-target X-ray model could be
made to fit the radio data.
@--------------------------------------------------------------------
Title: A Search for Solar Oscillations in the Solar
Chromosphere Using Millimeter Interferometric
Observations
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 1991BAAS...23R1033K
Abstract
@--------------------------------------------------------------------
Title: Millimeter Imaging of Energetic Electrons in Solar
Flares in Conjunction with GRO Experiments
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 1991BAAS...23Q1073K
Abstract
@--------------------------------------------------------------------
Title: Global Streamer Evolution
Authors: Thejappa, G.; Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1991BAAS...23.1045T
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of Radio Filaments
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
Bibliographic Code: 1991BAAS...23.1045G
Abstract
@--------------------------------------------------------------------
Title: Multifrequency Observations of a Remarkable Solar
Radio Burst
Authors: White, S. M.; Kundu, M. R.; Bastian, T. S.;
Gary, D. E.; Hurford, G. J.; Kucera, T.;
Bieging, J. H.
Bibliographic Code: 1991BAAS...23.1043W
Abstract
@--------------------------------------------------------------------
Title: Strong magnetic fields and inhomogeneity in the
solar corona
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1991ApJ...366L..43W
Abstract
It is shown that fields of 1800 G can exist in the corona based on
observations of gyroresonance emission at 15 GHz at coronal
temperatures. The strong fields occur in a small source radiating in the
extraordinary (x) mode over the penumbra of a large symmetric sunspot.
The optically-thin ordinary mode emission from the region shows a nearby
peak at only 36,000 K which may be due to a sunspot plume, and a hole
over the umbra consistent with the expected low-density material there.
The x-mode source is highly asymmetric, despite the apparent symmetry of
the sunspot, and its appearance and location imply that the strongest
magnetic fields in the corona are localized in a compact flux tube.
@--------------------------------------------------------------------
Title: Association of a Type IV Burst with a Slow CME
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1991max..conf..139G
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of Active Region 5555 During the
1st Max'91 Campaign
Authors: Schmahl, E. J.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1991max..conf...23S
Abstract
@--------------------------------------------------------------------
Title: Millimeter Solar Observing with BIMA
Authors: Kundu, M. R.; White, S. M.; Welch, W. J.
Bibliographic Code: 1991max..conf...11K
Abstract
@--------------------------------------------------------------------
Title: Millimeter Interferometric Observations of Solar
Flares During the SOLAR-A Mission
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 1991LNP...387..338K
Abstract
We present the results of the first high-spatial-resolution
interferometric observations of solar flares at millimeter wavelengths,
carried out with the Berkeley-Illinois-Maryland Array (BIMA). The
observations represent an improvement of an order of magnitude in both
sensitivity and spatial resolution compared with previous solar
observations at these wavelengths. Most of the flares occurring within
the field of view during the observations have been detected by BIMA,
including both very impulsive and longer-duration events. It appears
that millimeter burst sources are not much smaller than microwave
sources. If the emission in the flash phase is predominantly due to
gyrosynchrotron emission, we can rule out thermal gyrosynchrotron models
for the radio emission because the flux at millimeter wavelengths is too
high. During the Solar-A mission we plan to obtain both imaging data as
well as dedicated patrol observations of flare time profiles at
millimeter wavelengths.
@--------------------------------------------------------------------
Title: High spatial resolution observations of solar flares
at 3.3 MM wavelength
Authors: Kundu, M. R.; White, S. M.; Welch, W. J.;
Bieging, J. H.
Bibliographic Code: 1991AdSpR..11...91K
Abstract
The first high-spatial-resolution interferometric observations of solar
flares at millimeter wavelengths are presented. They are of high
sensitivity, and events ranging from subflares to X-class flares were
detected. One to three baselines with fringe spacings of 2 to 5 arcsec
were available, which demonstrated that generally source sizes were in
excess of 2 arcsec, but in some events the sources may be about 1
arcsec.
@--------------------------------------------------------------------
Title: Meter-decameter observations of dMe flare stars with
the Clark Lake Radio telescope
Authors: Jackson, P. D.; Kundu, M. R.; Kassim, N.
Bibliographic Code: 1990SoPh..130..391J
Abstract
The now-closed Clark Radio Observatory was used in 1984 and 1985 to
search for flaring emission from a number of dMe flare stars in the 30.9
to 110.6 MHz frequency range. No emission was found to greatly exceed
detection limits which range from about 1 Jy for 1 hr averaging, to
about 50 Jy for 1 s averaging, even though flares were often seen to
tens of mJy at 20 cm using the VLA for those times when VLA-CLRO
observations were coordinated. There are marginal detections of flaring
from AD Leo over two periods on December 15, 1985 which mark the
beginning and the end of a long-lasting, narrow-band flare at 1415 MHz.
@--------------------------------------------------------------------
Title: The observation of an unusually fast type IV
plasmoid
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1990ApJ...365L..31G
Abstract
A moving type IV burst of the 'isolated source' type has been detected
whose out-of-plane speed, at 1600 km/sec, becomes about 2800 km/sec upon
assumption of radial motion; this is twice as high as previously
reported speeds for bursts of this type. While shock waves are known to
have such high speeds, and a shock wave is likely to form ahead of a
high-speed plasmoid, no radio signature has been observed for such a
shock. This lack of shock detection may, however, be primarily due to
poor observing conditions. Energetic electrons, trapped in an about 1.4
G magnetic field of the plasmoid, can adequately account for the
emission.
@--------------------------------------------------------------------
Title: UVSP and VLA observations of the 24 June 1980 flare
- Asymmetric or isotropic beaming?
Authors: Kundu, M. R.; Schmahl, E. J.; Cheng, C. C.
Bibliographic Code: 1990SoPh..129..343K
Abstract
Observations of the 15:22 UT flare of June 24, 1980 were made using the
VLA at 6 cm wavelength simultaneously with the Hard X-Ray Imaging
Spectrometer (HXIS) aboard the Solar Maximum Mission. It was found that
at the peak of the impulsive phase, the brightest microwave point
appeared to lie between the soft (3.6-8.0 keV) and hard (22-30 keV)
X-ray maxima, which were themselves separated by about 20 arcsec. Since
the publication of these results, the imaging data from the Ultraviolet
Spectrometer Polarimeter (UVSP) have been analyzed with the goal of
narrowing the possible interpretations of the event. Like the VLA and
HXIS, the UVSP observations provide information about the location of
the primary electrons; the observations taken together suggest that the
fast electrons were symmetrically distributed within the flare loop.
@--------------------------------------------------------------------
Title: Book-Review - Energetic Phenomena on the Sun
Authors: Kundu, M. R.; Woodgate, B.; Schmahl, E. J.;
Staude, J.
Bibliographic Code: 1990AN....311..416K
Abstract
@--------------------------------------------------------------------
Title: Filament eruption and storm radiation at
meter-decameter wavelengths
Authors: Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1990SoPh..129..133K
Abstract
In a weak noise storm observed by the Clark Lake multifrequency
radioheliograph at four frequencies, the noise storm onset was
associated with a filament eruption and a gradual rise and fall in soft
X-rays. The noise storm emission is compared with related emissions in
other wavelengths to develop a composite scenario of the event.
Superthermal particles with a temperature that is 10 times the coronal
electron temperature and a density of 0.001 times the coronal density
are adequate to explain the observed radiation. If the storm radiation
is affected in the same way as the quiet-sun emission by
inhomogeneities, the observed spectrum can be interpreted as due to
propagation effects.
@--------------------------------------------------------------------
Title: Multiple moving magnetic structures in the solar
corona
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1990SoPh..128..377G
Abstract
This paper reports the study of moving magnetic structures inferred from
the observations of a moving type IV event with multiple sources. The
ejection contains at least two moving radio emitting loops with
different relative inclinations. The radio loops are located above
multiple H-alpha flare loops in an active region near the limb. The
relationship between the two systems of loops is investigated. The
spatial, temporal, and geometrical associations between the radio
emission and near surface activities suggest a scenario similar to
coronal mass ejection (CME) events, although no CME observations exist
for the present event. From the observed characteristics, it is found
that the radio emission can be interpreted as Razin suppressed optically
thin gyrosynchrotron emission from nonthermal particles of energy about
100 keV and density about 100-100,000/cu cm in a magnetic field not
greater than 2 G.
@--------------------------------------------------------------------
Title: First high spatial resolution interferometric
observations of solar flares at millimeter
wavelengths
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.;
Bieging, J. H.; Hurford, G. J.
Bibliographic Code: 1990ApJ...358L..69K
Abstract
The first high spatial resolution interferometric observations of solar
flares at millimeter wavelengths, carried out with the
Berkeley-Illinois-Maryland Array are presented. The observations were
made at 3.3 mm wavelength during the very active periods of March 1989,
using one or three baselines with fringe spacings of 2-5 arcsec. The
observations represent an improvement of an order of magnitude in both
sensitivity and spatial resolution compared with previous solar
observations at these wavelengths. It appears that millimeter burst
sources are not much smaller than microwave sources. The most intense
bursts imply brightness temperatures of over 10 to the 6th K and are due
to nonthermal gyrosynchrotron emission or possibly thermal free-free
emission. If the emission in the flash phase is predominantly due to
gyrosynchrotron emission, thermal gyrosynchrotron models can be ruled
out for the radio emission because the flux at millimeter wavelengths is
too high.
@--------------------------------------------------------------------
Title: Microwave and X-ray observations of a major confined
solar flare
Authors: Schmahl, E. J.; Schmelz, J. T.; Saba, J. L. R.;
Strong, K. T.; Kundu, M. R.
Bibliographic Code: 1990ApJ...358..654S
Abstract
Observations of an X4 flare of May 19, 1984 using the VLA and the SMM
X-ray Polychromator are discussed. The 6 cm radio source remained
stationary throughout the decay phase. Combined with other evidence,
this indicates that the flare was magnetically confined and did not
disrupt the complex structure of its region. The observed structures may
be associated with a neutral sheet connecting the two bipoles.
@--------------------------------------------------------------------
Title: Microbursts at meter-decameter wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1990SoPh..127..165T
Abstract
The characteristics of microbursts are studied using a large data base
obtained with the multifrequency radioheliograph of the Clark Lake Radio
Observatory. Most of the new observations were made from July 29, 1985
to August 2, 1985. Characteristis such as frequency drift, source size,
and brightness temperature are compared with the properties of normal
type III bursts. It is found that (1) the brightness temperature is in
the range 0.6-60 million K, and (2) the drift rate of the microbursts is
slightly smaller than that of normal type III bursts, implying electron
beams with speeds of about 0.2c. The microbursts can be explained as due
to Langmuir waves spontaneous emitted by electron beams, whereas normal
type III bursts are due to coherently emitted plasma waves in a
two-stream instability.
@--------------------------------------------------------------------
Title: High-Dynamic-Range Multifrequency Radio Observations
of a Solar Active Region
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1990BAAS...22R.794W
Abstract
@--------------------------------------------------------------------
Title: Magnetic Field Strengths in Post-Flare Loop Systems
Authors: Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1990BAAS...22Q.827S
Abstract
@--------------------------------------------------------------------
Title: CoMStOCI: Physical Properties of an Active Region
Loop Observed at the Solar Limb
Authors: Holman, G. D.; Brosius, J. W.; Nitta, N.;
White, S. M.; Kundu, M. R.; Gopalswamy, N.;
Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.
Bibliographic Code: 1990BAAS...22..899H
Abstract
@--------------------------------------------------------------------
Title: Millimeter-Interferometer Observations of Solar
Flares
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.;
Bieging, J. H.; Hurford, G. J.
Bibliographic Code: 1990BAAS...22..823K
Abstract
@--------------------------------------------------------------------
Title: Evolution of Active Regions at 20 cm
Authors: Gopalswamy, N.; White, S. M.; Kundu, M. R.
Bibliographic Code: 1990BAAS...22..795G
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of Solar Active Regions at 6 and 20
cm During the Spacelab 2 Mission
Authors: Alissandrakis, C. E.; Kundu, M. R.;
Shevgaonkar, R. K.
Bibliographic Code: 1990BAAS...22..795A
Abstract
@--------------------------------------------------------------------
Title: New Observations of Storm Radiation at Decameter
Wavelengths and Their Interpretation
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1990BAAS...22..794T
Abstract
@--------------------------------------------------------------------
Title: Kilometric shock-associated events and microwave
bursts
Authors: Kundu, M. R.; MacDowall, R. J.; Stone, R. G.
Bibliographic Code: 1990Ap&SS.165..101K
Abstract
The peak times of impulsive microwaves bursts are compared with those of
shock-associated (SA) kilometric radio events. The first peaks in these
two frequency regimes are usually well-correlated in time, but the last
peaks of the SA events observed at 1 MHz occur an average of 20 min
after the last impulsive microwave peaks. In some cases, the SA events
overlap in time with the post-burst increases of microwave bursts;
sometimes there is general correspondence in their intensity time
profiles. These observations suggest that the earlier components of the
SA events are usually caused by electrons accelerated in or near the
microwave source region. The possibility that the later components of
some SA events could be associated with nonthermal electrons responsible
for microwave post-burst increases, although they have traditionally
been attributed to electrons accelerated at type II burst producing
shocks in the upper corona is discussed.
@--------------------------------------------------------------------
Title: The solar probe mission
Authors: Feldman, W. C.; Anderson, J.; Bohlin, J. D.;
Burlaga, L. F.; Farquhar, R.; Gloeckler, G.;
Goldstein, B. E.; Harvey, J. W.; Holzer, T. E.;
Jones, W. V.; Kellogg, P. J.; Krimigis, S. M.;
Kundu, M. R.; Lazarus, A. J.; Mellott, M. M.;
Parker, E. N.; Rosner, R.; Rottman, G. J.;
Slavin, J. A.; Suess, S. T.; Tsurutani, B. T.;
Woo, R. T.; Zwickl, R. D.
Bibliographic Code: 1990AIPC..203..101F
Abstract
The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs
perihelion solar polar orbit (with the first perihelion passage in 2004)
to explore in situ one of the last frontiers in the solar system-the
solar corona. This mission is both affordable and technologically
feasible. Using a payload of 12 (predominantly particles and fields)
scientific experiments, it will be possible to answer many
long-standing, fundamental problems concerning the structure and
dynamics of the outer solar atmosphere, including the acceleration,
storage, and transport of energetic particles near the Sun and in the
inner (<65 Rs) heliosphere.
@--------------------------------------------------------------------
Title: Measurement of solar magnetic fields from radio
observations
Authors: Kundu, M. R.
Bibliographic Code: 1990MmSAI..61..431K
Abstract
Measurements of magnetic fields in the sun's atmosphere using radio
observations are discussed. Radio measurements of magnetic fields in the
chromosphere and the corona are indirect. In the chromosphere, these are
based upon the measurement of polarization of active regions at
millimeter wavelengths. In the transition region and the corona, the
properties of gyroresonance radiation of active regions at centimeter
wavelengths are used. Total intensity and polarization maps and modeling
are used to determine which harmonic (second or third) is predominant in
the active region emission. A direct method of measuring coronal
magnetic fields using cyclotron line emission is discussed, and the
relevant data as presently available are presented.
@--------------------------------------------------------------------
Title: Some problems in low frequency solar radio physics
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1990LNP...362...97G
Abstract
At present, there is virtually no information in a hight range of 4 to
10 solar radii, the range that may be the region where the solar wind
originates and the magnetic field configuration of the corona changes
from predominantly closed to open. This paper discusses some of the
issues which emerge from the meter-decameter studies of the sun which
could probably be resolved by acquiring imaging data at frequencies
below 25 MHz. These include the characteristics of storm radiations, the
origin of type II shocks, and the origin of type III bursts.
@--------------------------------------------------------------------
Title: The sun at the VLA's metric and decimetric
wavelengths
Authors: White, S. M.; Kundu, M. R.; Gopalswamy, N.;
Schmahl, E. J.
Bibliographic Code: 1990IAUS..142..523W
Abstract
Preliminary results of solar observations at 0.333 and 1.5 GHz made with
the VLA during the September 11-17, 1988 period are presented.
Generally, there are few structural changes in the active region sources
from one day to the next, suggesting that structural evolution is
relatively slow. Contour maps at 1.5 GHz are presented for each of the
four days. Two noise storms were present at 0.33 GHz all week and were
highly polarized.
@--------------------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1990IAUS..142..521T
Abstract
@--------------------------------------------------------------------
Title: Dual frequency variability study of an active region
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1990IAUS..142..489S
Abstract
The VLA is used to investigate a short-time variability of a solar
region at 6 and 2 cm wavelengths simultaneously. The observed low
brightness temperatures indicate that the emission is mainly originating
from the chromosphere-corona transition region. It is shown that an
independent variation of a few percent in the magnetic field (900 +/- 45
G) and a factor-of-two variation in the density (2 to 4 x 10 exp 10/cu
cm) over a time scale of a few hours is required to explain the
uncorrelated brightness temperature at the two wavelengths.
@--------------------------------------------------------------------
Title: Millimeter and microwave activity of the sun
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 1990IAUS..142..457K
Abstract
Preliminary results of high-spatial-resolution millimeter observations
of recent solar flares carried out with the Berkeley-Illinois-Maryland
Array are presented. Findings obtained from multifrequency observations
using the VLA are reported. The time profiles of several bursts during
March 1989 are presented. Most of the bursts were impulsive and
short-lived, and a number of longer-duration bursts were observed as
well. All the bursts were fairly weak, with none exceeding 1 sfu of
correlated amplitude. A number had rise times less than the available
resolution of 10 sec. VLA observations in September 1988 showed that
there is exceptionally good correspondence between the 1.5-GHz radio
sources and the regions which are dark in He 10830 images and bright in
Ca images.
@--------------------------------------------------------------------
Title: The radio spectra of RS CVn stars
Authors: White, S. M.; Kundu, M. R.; Uchida, Y.; Nitta, N.
Bibliographic Code: 1990ASPC....9..239W
Abstract
The results of observations of several systems are presented for the
0.327-90 GHz range to study the radio coronae and outbursts associated
with the RS CVn stars, as well as their visibility at millimeter
wavelengths. The radio spectra are observed with the VLA and the
Nobeyama 45-m millimeter-wavelength telescope. The three stars observed
with the Nobeyama and VLA telescopes are UX Ari, AR Lac, and HR 5110,
and the frequencies and conditions of the nonsimultaneous observations
are set forth. Observations of the RS CVn systems at mm wavelengths is
possible, and it is theorized that important information regarding
flares and energy release can be derived from these data. A simple model
is presented for the radio-coronae source related to outbursts of up to
5 GHz, and the onset of outbursts are predicted to be accompanied by low
frequency type-II plasma emission.
@--------------------------------------------------------------------
Title: Magnetic field reconnection in solar and stellar
flares
Authors: Kundu, M. R.; White, S. M.
Bibliographic Code: 1990AdSpR..10...85K
Abstract
Evidence for magnetic reconnection in both solar and stellar flares is
derived from radio observations. Two cases in which solar flares were
observed by VLA are represented, showing the interacting magnetic
structures that lead to a flare. The cases are discussed, noting the
aspects of the cases which support the hypothesis of magnetic
reconnection. Also, consideration is given to indirect evidence based on
flares in the coronae of red dwarf stars.
@--------------------------------------------------------------------
Title: Book Review: Energetic phenomena on the sun /
Kluwer, 1989
Book Authors: Kundu, M. R.; Woodgate, B.; Schmahl, E. J.
Bibliographic Code: 1989Ap&SS.162..175K
Abstract
@--------------------------------------------------------------------
Title: Simple non-thermal models for the quiescent radio
emission of dMe flare stars
Authors: White, S. M.; Kundu, M. R.; Jackson, P. D.
Bibliographic Code: 1989A&A...225..112W
Abstract
Simple nonthermal gyrosynchrotron models were applied to the quiescent
emission of M dwarf stars. Evidence is presented which suggests that
these stars have a number of smaller active regions contributing to the
observed flux. The evidence includes an absence of Zeeman polarization
in optical observations and a lack of polarization in quiescent
emission.
@--------------------------------------------------------------------
Title: Limb Passage of a Microwave Source
Authors: Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1989BAAS...21R1145S
Abstract
@--------------------------------------------------------------------
Title: Evidence for Noise Storm Emission by Superthermal
Particles During a Filament Eruption
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989BAAS...21.1146G
Abstract
@--------------------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Thejappa, G.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989BAAS...21.1145T
Abstract
@--------------------------------------------------------------------
Title: Radio Observations of Coronal Changes
Authors: Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1989BAAS...21.1145K
Abstract
@--------------------------------------------------------------------
Title: Time variability of solar active regions at
centimeter wavelengths
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1989ApJ...342..586S
Abstract
An analysis is presented of the variability of centimeter wavelength
emission originating from the solar transition region and lower corona,
and the variability is compared with the sun's quiescent emission.
Sequential dual wavelength observations are presented and used to put
constraints on a possible model of the variability of active region
emissions and to better understand the dynamics of active regions. It is
shown that gyroresonance emission contributes significantly to the
active region emission at 6 cm, whereas all the quiet-sun emission can
be attributed to free-free emission. From comparison of the quiet-sun
and active region models, it is shown that the density at the base of
the transition region is higher in active regions.
@--------------------------------------------------------------------
Title: Radioheliograph and white-light coronagraph studies
of a coronal mass ejection event
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989SoPh..122..145G
Abstract
The radioheliograph and SMM-C/P observations of November 3, 1986 mass
ejection event are analyzed. The metric radio emissions are the only
detected activity associated with the mass ejection, but are adequate to
study the evolution of the event. The start time of the ejection seems
to precede a possible flare behind the limb indicated by the early type
III bursts. The physical relation between various types of bursts and
the CME is studied, interpreting moving type IV bursts as a plasma
emission process. It is also shown using white-light coronagraph data
that the density in the source region of the moving type IV is
sufficient to support second-harmonic plasma emission at the observed
frequency of 50 MHz.
@--------------------------------------------------------------------
Title: A slowly moving plasmoid associated with a filament
eruption
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989SoPh..122...91G
Abstract
Imaging observations of a slowly moving type IV burst associated with a
filament eruption are reported. This event was preceded by weak type III
burst activity and was accompanied by a quasi-stationary continuum that
persisted for several hours. The starting times and speeds of moving
type IV burst and the erupting filament are nearly the same, implying a
close physical relation between the two. The moving type IV burst is
interpreted as gyrosynchrotron emission from a plasmoid containing a
magnetic field of 1-2 G and nonthermal electrons of density (0.1-1) x 10
to the 6th/cu cm with a relatively low average energy of about 50 keV.
@--------------------------------------------------------------------
Title: Simultaneous multi-frequency imaging observations of
solar microwave bursts
Authors: Kundu, M. R.; White, S. M.; Schmahl, E. J.
Bibliographic Code: 1989SoPh..121..153K
Abstract
The results of simultaneous two-frequency imaging observations of solar
microwave bursts with the Very Large Array are reviewed. Simultaneous 2
and 6 cm observations have been made of bursts which are optically thin
at both frequencies, or optically thick at the lower frequency. In the
latter case, the source structure may differ at the two frequencies, but
the two sources usually seem to be related. However, this is not always
true of simultaneous 6 and 20 cm observations. The results have
implications for the analysis of nonimaging radio data of solar and
stellar flares.
@--------------------------------------------------------------------
Title: Meter Wave Radio Signatures of Slow CME's and
Coronal Streamer Evolution
Authors: Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1989BAAS...21R.857K
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of a Small Impulsive Flare
Authors: White, S. M.; Kundu, M. R.; McConnell, D.
Bibliographic Code: 1989BAAS...21R.834W
Abstract
@--------------------------------------------------------------------
Title: Partially Occulted Microwave and X-ray Flares
Authors: Schmahl, E. J.; Kundu, M. R.; Tappin, J.;
Simnett, G.
Bibliographic Code: 1989BAAS...21Q.834S
Abstract
@--------------------------------------------------------------------
Title: Joule Heating and Runaway Electron Acceleration in a
Solar Flare
Authors: Holman, G. D.; Kundu, M. R.; Kane, S.
Bibliographic Code: 1989BAAS...21..864H
Abstract
@--------------------------------------------------------------------
Title: The Sun at the VLA's Meter and Decimeter Wavelengths
Authors: White, S. M.; Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989BAAS...21..861W
Abstract
@--------------------------------------------------------------------
Title: The First Interferometric Observations with
Arc-Second Resolution of Solar Radio Bursts at
Millimeter Wavelengths
Authors: Kundu, M. R.; White, S. M.; Gopalswamy, N.;
Bieging, J. H.
Bibliographic Code: 1989BAAS...21..861K
Abstract
@--------------------------------------------------------------------
Title: Radio and Optical Observations of Moving Magnetic
Structures in the Solar Corona
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989BAAS...21..857G
Abstract
@--------------------------------------------------------------------
Title: Interpretation of Multiwavelength Observations of
Solar Active Regions Obtained During CoMStOC
Authors: Brosius, J. W.; Holman, G. D.; Nitta, N.;
White, S. M.; Kundu, M. R.; Gopalswamy, N.;
Schmelz, J. T.; Saba, J. R. L.; Willson, R.
Bibliographic Code: 1989BAAS...21..838B
Abstract
@--------------------------------------------------------------------
Title: Quiescent and flaring radio emission from the flare
stars AD Leonis, EQ Pegasi, UV Ceti, Wolf 630, YY
Geminorum and YZ Canis Minoris
Authors: Jackson, P. D.; Kundu, M. R.; White, S. M.
Bibliographic Code: 1989A&A...210..284J
Abstract
Observations of the flare stars AD Leo, EQ Peg, UV Cet, Wolf 630, YY
Gem, and YZ CMi at 6 and 20 cm wavelengths are presented. These
observations display how a sample of the more active radio flare stars
behave over periods of several hours. An extensive time analysis at five
minute resolution, to investigate the typical variability of these
stars, is presented together with a ten-second-resolution time analysis
for periods of enhanced activity. Highlights are the enhanced 6-cm
activity from both components of the UV Ceti system, quiescent emission
from UV Ceti at 20 cm (which has a higher flux than the quiescent
emission at 6 cm), the possible detection of polarized quiescent
emission, a 20-cm flare from AD Leo in which the polarization changes
sign during the rise phase of the flare, and a relatively high level of
6-cm emission from AD Leo.
@--------------------------------------------------------------------
Title: Microwave evidence for large-scale changes
associated with a filament eruption
Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q.-J.
Bibliographic Code: 1989ApJ...336.1078K
Abstract
VLA observations at 6 and 20 cm wavelengths taken on August 3, 1985 are
presented, showing an eruptive filament event in which microwave
emission originated in two widely separated regions during the
disintegration of the filament. The amount of heat required for the
enhancement is estimated. Near-simultaneous changes in intensity and
polarization were observed in the western components of the northern and
southern regions. It is suggested that large-scale magnetic
interconnections permitted the two regions to respond similarly to an
external energy or mass source involved in the disruption of the
filament.
@--------------------------------------------------------------------
Title: Largescale Magnetic Field Phenomena
Authors: Harrison, R. A.; Bentley, R. D.; Brosius, J.;
Dwivedi, B. N.; Jardine, M.; Klimchuk, J. A.;
Kundu, M. R.; Pearce, G.; Saba, J.; Sakurai, T.;
Schmahl, E. J.; Schmelz, J.; Sime, D. G.;
Steele, C. D. C.; Sun, M. T.; Tappin, S. J.;
Waljeski, K.; Wang, A. H.; Wu, S. T.
Bibliographic Code: 1989tnti.conf....1H
Abstract
@--------------------------------------------------------------------
Title: Recent results of meter-decameter wave observations
of solar flares.
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1989sasf.confP.185G
Abstract
The authors present recent results from meter-decameter imaging of
several classes of solar radio bursts: preflare activity in the form of
type III bursts, correlated type IIIs from distant sources, and type II
and moving type IV bursts associated with flares and CMEs.
@--------------------------------------------------------------------
Title: Non-thermal electrons and stellar radio emission.
Authors: White, S. M.; Kundu, M. R.
Bibliographic Code: 1989sasf.confP..37W
Abstract
Radio emission from dMe flare stars has both a flaring and a quiescent
component. When one compares stellar radio emission with the Sun,
however, one finds that the apparent brightness temperature of the
quiescent component often exceeds the temperature of non-thermal solar
radio flares, and so it is likely that stellar quiescent emission also
comes from non-thermal electrons. Here the authors briefly review the
observations of quiescent emission, argue that the emitting regions are
small, show that such small regions can still account for the observed
fluxes, and discuss the source of electrons.
@--------------------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.;
Dulk, G. A.; Emslie, A. G.; Enome, S.;
Gabriel, A. H.; Kundu, M. R.; Melrose, D.;
Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.;
Rieger, E.; Tanaka, K.; Zirin, H.
Bibliographic Code: 1989epos.conf..225C
Abstract
The work of this group was concerned with how the energy released in a
solar flare is transported through the solar atmosphere before escaping
in the form of radiant and mechanical energy.
@--------------------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.;
Murphy, R. J.; Alissandrakis, C.; Bai, T.;
Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.;
Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.;
MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.;
Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.;
Tsuneta, S.; van Hoven, G.
Bibliographic Code: 1989epos.conf..127V
Abstract
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons. 3. Phenomena associated with ions and
relativistic electrons in solar flares. 4. Theoretical studies of
particle acceleration. 5. Achievements - outstanding questions.
@--------------------------------------------------------------------
Title: Energetic phenomena on the Sun: Introduction.
Authors: Kundu, M. R.; Woodgate, B.
Bibliographic Code: 1989epos.conf.....K
Abstract
Contents: 1. Previous history. 2. The Solar Maximum Mission: objectives,
instruments, operations. 3. Summary of workshop results.
@--------------------------------------------------------------------
Title: Three dimensional structures of coronal streamers,
holes and CME plasmoids from multifrequency imaging
observations
Authors: Kundu, M. R.; Schmahl, E. J.; Gopalswamy, N.;
White, S. M.
Bibliographic Code: 1989AdSpR...9R..41K
Abstract
Throughout the quiet sun years 1982-1987, the Clark Lake Radioheliograph
routinely mapped the solar corona on a daily basis at frequencies from
30 to 100 MHz. The Clark Lake maps show a variety of features which have
been analyzed quantitatively, providing information about the three
dimensional nature of large scale structures of the solar corona.
@--------------------------------------------------------------------
Title: Modelling a C-type flare observed in microwaves and
hard X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, Brian R.
Bibliographic Code: 1988fnsm.work..246S
Abstract
Using the very large array (VLA) at 6 and 20 cm wavelength and the hard
X-ray burst spectrometer on the Solar Maximum Mission, a two-ribbon
flare was observed from the onset phase through the maximum and decline
on November 14, 1981. Because of the extensive size of the microwave
source and the gradual variations in hard X-rays whose spectrum becomes
progressively flatter with time, the flare is classified as a C-type
flare. Considering the hardening of the X-ray spectrum and its
non-impulsive nature, a coronal trap model was invoked for the energetic
electrons. The microwave emission is easily accounted for by
gyrosynchronous radiation from mildly relativistic electrons. It was
found that the source must be optically thick at 20 cm during the
maximum phase, but as the source evolved toward an optically thin
regime, the intensity decreased while the degree of circular
polarization increased. In an initial homogeneous model, we found that
the computed microwave spectrum was too narrow to match the patrol
spectrum from 606 to 15400 MHz. In the model, the magnetic field
consists of a dipolar arcade bridging the H alpha ribbons, and extending
to heights of order 40,000 to 50,000 km. The variation of the magnetic
field strength from footpoints to apex causes the gyrosynchrotron
spectrum to be broader. Preliminary conclusions regarding the electron
distributions producing the hard X-rays and the microwaves, and the
suitability of this model for C-type flares is presented.
@--------------------------------------------------------------------
Title: Millimeter wavelength observations of solar flares
for Max 1991
Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.;
Schmahl, E. J.; White, S. M.; Welch, W. J.
Bibliographic Code: 1988fnsm.work..107K
Abstract
The Hat Creek millimeter-wave interferometer (to be known as the
Berkeley-Illinois-Maryland Array, BIMA) is being upgraded. The improved
array will become available during the coming solar maximum, and will
have guaranteed time for solar observing. The Hat Creek millimeter-wave
interferometer is described along with the improvements. The scientific
objectives are briefly discussed.
@--------------------------------------------------------------------
Title: Detection of the dMe flare star YZ Canis Minoris
simultaneously at 20 and 90 centimeter wavelengths
Authors: Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1988ApJ...334.1001K
Abstract
The first aperture synthesis detection of the flare star YZ CMi at 90 cm
wavelength is presented here. The simultaneous observations carried out
at 20 and 90 cm wavelengths show that the emission at the two
wavelengths is unipolar in the same sense and is uncorrelated. The high
brightness temperature of ≡1013K at 90 cm wavelength
strongly supports the coherent nature of the emission. The authors
propose that the coherent emission is intrinsically unpolarized and the
polarization is introduced by absorption in the higher coronal levels
with large-scale magnetic fields, presumably the dipole magnetic field.
@--------------------------------------------------------------------
Title: Variability of metric emission from the sun
Authors: Shevgaonkar, R. K.; Kundu, M. R.; Jackson, P. D.
Bibliographic Code: 1988ApJ...329..982S
Abstract
Full-disk observations of the sun obtained with the VLA at 317 MHz have
been analyzed, with special attention being given to the short period
variability of the meter-wavelength sources. A reduction in brightness
is noted over coronal holes at 90 cm. Thermal emission models for the
slowly varying component are investigated, along with a nonthermal
emission mechanism for storm radiation at meter wavelengths. The results
indicate that the thermal model encounters difficulties in accommodating
short period changes over a few tens of minutes, and that the nonthermal
mechanism encounters difficulty in accounting for the variability of low
brightness temperatures of less than 10 to the 6th K. A gyrotron
synchrotron emission mechanism has been ruled out.
@--------------------------------------------------------------------
Title: Current Loop Coalescence Model of Solar Flares:
Erratum
Authors: Tajima, T.; Sakai, J.; Nakajima, H.; Kosugi, T.;
Brunel, F.; Kundu, M. R.
Bibliographic Code: 1988ApJ...329..517T
Abstract
@--------------------------------------------------------------------
Title: High resolution microwave and X-ray observations of
solar flares
Authors: Alissandrakis, C. E.; Schadee, A.; Kundu, M. R.
Bibliographic Code: 1988A&A...195..290A
Abstract
This paper presents an analysis of high spatial resolution observations
of 18 weak flares, carried out during the Solar Maximum Year in the
microwave range, H-alpha, and soft X-rays, together with observations of
the associated hard X-ray emission and the photospheric magnetic field.
This combination of observations made it possible to obtain a picture of
the flare geometry and the relative position of the various emissions,
to study the change of the geometry during the flare, to estimate the
electron temperature and emission measure of the thermal plasma, and to
compute the contribution of the free-free process in the microwave
emission. Results are interpreted as evidence for the presence of
energetic electrons even in the post-burst phase of some flares. There
was also found a clear case of homologous radio and X-ray bursts, one
case of foot-point expansion with a relative velocity of 20 km/s at 6.16
cm, as well as some evidence of triggering of flares by disturbances
moving with a velocity of 5000-13,000 km/s.
@--------------------------------------------------------------------
Title: Co-ordinated VLA and EXOSAT observations of the
flare stars UV Ceti, EQ Pegasi, YZ Canis Minoris,
and AD Leonis
Authors: Kundu, M. R.; White, S. M.; Jackson, P. D.;
Pallavicini, R.
Bibliographic Code: 1988A&A...195..159K
Abstract
The authors have observed four flare stars (UV Cet, EQ Peg, YZ CMi and
AD Leo) simultaneously with the VLA and the EXOSAT satellite over
continuous periods of 7 - 10 h. This is the first time that flare stars
were observed simultaneously in X-rays and at microwave frequencies with
high sensitivity instrumentation. All stars were detected both at the
quiescent level and during flares. Although considerable activity in
both X-rays and in the radio was found, there was little correlation
between the two wavelength domains. The auhors discuss the significance
of these observations for coronal activity in red dwarf flare stars.
@--------------------------------------------------------------------
Title: A study of coronal bright points at 20 CM wavelength
Authors: Nitta, N.; Kundu, M. R.
Bibliographic Code: 1988SoPh..117...37N
Abstract
The authors present the results of a study of coronal bright points
(B.P.) observed at 20 cm with the VLA on a day when the Sun was
exceptionally quiet. Microwave maps of B.P. were obtained using data for
the entire observing period of 5 hours, as well as for shorter periods
of a few minutes. Most B.P., especially those appearing in the
full-period maps appear to be associated with small bipolar structures
on the photospheric magnetogram. Overlays of B.P. maps on the
Ca+K picture, show that the brightest part of a B.P. tends to
lie on the boundary of a supergranulation network. In general, the
bright points exhibit rapid variations in intensity. There is no
systematic correlation between the size of a B.P. and its intensity; the
apparently slow variation of B.P. emission may have rapid fluctuations
superimposed on it.
@--------------------------------------------------------------------
Title: Modelling a C-Type Flare Observed in Microwaves and
Hard X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
Bibliographic Code: 1988BAAS...20R.748S
Abstract
@--------------------------------------------------------------------
Title: Moving Radio Loop Structure During a Fast CME
Authors: Gopalswamy, N.; Kundu, M. R.; Hundhausen, A.
Bibliographic Code: 1988BAAS...20Q.682G
Abstract
@--------------------------------------------------------------------
Title: Millimeter Wavelength Observations of Solar Flares
for Max'91
Authors: Kundu, M. R.; Gopalswamy, N.; Nitta, N.;
Schmahl, E. J.; White, S. M.
Bibliographic Code: 1988BAAS...20..746K
Abstract
@--------------------------------------------------------------------
Title: Slowly-Varying Observed with the Clark Lake
Radioheliograph
Authors: Schmahl, E. J.; Kundu, M. R.; Gopalswamy, N.;
Jackson, P. D.
Bibliographic Code: 1988BAAS...20..712S
Abstract
@--------------------------------------------------------------------
Title: A VLA Survey of dM Stars Covering a Broad Range in
X-ray Fluxes
Authors: Kundu, M. R.; White, S. M.; Agrawal, P. C.
Bibliographic Code: 1988BAAS...20..696K
Abstract
@--------------------------------------------------------------------
Title: Coronal bright points at 6 and 20 centimeter
wavelengths
Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q.-J.
Bibliographic Code: 1988ApJ...325..905K
Abstract
The paper presents the results of near-simultaneous observations of
bright points at 6 and 20 cm for a time interval of 10 hr using the VLA.
It is shown that, at both 6 and 20 cm, the radio sources in the quiet
sun have a very close association with bipolar features seen in
magnetograms and with dark features in He I 10830 A spectroheliograms.
The paper discusses the associations and the distributions of size,
brightness, and temporal variation of the microwave bright points. It is
found that the brightness temperatures of the 6 and 20 cm bright points
are in the approximate ratio 0.09:1 expected from the emission mechanism
being thermal bremsstrahlung.
@--------------------------------------------------------------------
Title: Coronal bright points at 6cm wavelength
Authors: Fu, Qijun; Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1988VA.....31..103F
Abstract
Results are presented from observations of bright points at a wavelength
of 6-cm using the VLA with a spatial resolution of 1.2 arcsec. During
two hours of observations, 44 sources were detected with brightness
temperatures between 2000 and 30,000 K. Of these sources, 27 are
associated with weak dark He 10830 A features at distances less than 40
arcsecs. Consideration is given to variations in the source parameters
and the relationship between ephemeral regions and bright points.
@--------------------------------------------------------------------
Title: Variability of meter wavelength solar radio emission
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1988sscd.conf..248S
Abstract
The VLA at 317 MHz is used to study the variability of meter wavelength
sources, and the results are reported. Simultaneous decametric
observations using the Clark Lake radioheliograph are also presented.
The meter wavelength sources show a variation in brightness temperature
of a few times 100,000 K over timescales of a few tens of minutes. The
decametric sources show much more rapid variability in brightness and
spatial location. The mechanisms of thermal emission, gyrosynchrotron
emission, and plasma emission are used to explain the short time
variability of the meter wavelength sources. It is argued that low
magnetic fields in the corona suppress gyrosynchrotron emission and that
if the brightness temperature is due to free-free emission, a change in
volume emission measure of about 4 x 10 to the 47th/cu cm or a rate of
change of thermal energy of about 10 to the 25th ergs/s is required to
explain the variability.
@--------------------------------------------------------------------
Title: Coronal bright points in microwaves
Authors: Kundu, M. R.; Nitta, N.
Bibliographic Code: 1988sscd.conf...89K
Abstract
An excellent map of the quiet sun showing coronal bright points at 20-cm
wavelength was produced using the VLA on February 13, 1987. The
locations of bright points (BPs) were studied relative to features on
the photospheric magnetogram and Ca K spectroheliogram. Most bright
points appearing in the full 5-hour synthesized map are associated with
small bipolar structures on the photospheric magnetogram; and the
brightest part of a BP tends to lie on the boundary of a
supergranulation network. The bright points exhibit rapid variations in
intensity superposed on an apparently slow variation.
@--------------------------------------------------------------------
Title: Quasi-dedicated millimeter wave imaging observations
of solar flares during next solar maximum
Authors: Kundu, M. R.
Bibliographic Code: 1988AdSpR...8...33K
Abstract
A brief description of the Berkeley-Illinois-Maryland Millimeter Array
for synthesis mapping of the sun and the other sources is given. The
array will be used in a quasi-dedicated mode to observe solar flares.
The main scientific objectives are to obtain positional and structural
information of millimeter solar bursts, and to study high energy flare
physics and the role of electron beams in producing H-alpha, EUV and
white light emission.
@--------------------------------------------------------------------
Title: Current loop coalescence model of solar flares [
Erratum: 1988ApJ...329..517T ]
Authors: Tajima, T.; Sakai, J.; Nakajima, H.; Kosugi, T.;
Brunel, F.; Kundu, M. R.
Bibliographic Code: 1987ApJ...321.1031T
Abstract
A computer simulation and theoretical study of the physical
characteristics of the explosive coalescence of current-carrying loops
is presented. Characteristics of the explosive coalescence include a
large impulsive increase of the kinetic energies of electrons and ions,
the simultaneous heating and acceleration of electrons and ions in high
and low energy ranges, and a break in the energy spectra of electrons
and ions. A characteristic double subpeak structure is found in the
quasi-periodic oscillations found in the time profiles of the solar
flares of June 7, 1980 and November 26, 1982 which can be explained in
terms of the coalescence instability of two current loops.
@--------------------------------------------------------------------
Title: Simultaneous 2 and 6 centimeter wavelength
observations of a solar flare using the VLA
Authors: Kundu, M. R.; Velusamy, T.; White, S. M.
Bibliographic Code: 1987ApJ...321..593K
Abstract
VLA observations of a solar active region and a flare are discussed. The
event was observed at wavelengths of 2 and 6 cm simultaneously. Radio
maps prior to the flare delineate the most important magnetic structures
in the region. Interaction between these structures apparently led to
preheating of plasma above the active region some 30 minutes prior to
the flare. The 2 and 6 cm flare positions were coincident, and the time
profiles of the burst at the two wavelengths were almost identical,
implying that the same population of electrons was responsible for
emission at the two wavelengths. Emission was probably nonthermal
gyrosynchrotron radiation, and the physical conditions in the burst
source are derived using this assumption.
@--------------------------------------------------------------------
Title: Simultaneous radio and white light observations of
the 1984 June 27 coronal mass ejection event
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1987SoPh..114..347G
Abstract
The authors present the two-dimensional imaging observations of radio
bursts in the frequency range 25 - 50 MHz made with the Clark Lake
multifrequency radioheliograph during a coronal mass ejection event
(CME) observed on 1984, June 27 by the SMM Coronagraph/Polarimeter and
Mauna Loa K-coronameter. The event was spatially and temporally
associated with precursors in the form of meter-decameter type III
bursts, soft X-ray emission and a Halpha flare spray. The observed
type IV emission in association with the CME (and the Halpha spray)
could be interpreted as gyrosynchrotron emission from a plasmoid
containing a magnetic field of ≡2.5 G and nonthermal electrons
with a number density of ≡105cm-3 and energy
⪆350 keV.
@--------------------------------------------------------------------
Title: A study of solar preflare activity using
two-dimensional radio and SMM-XRP observations
Authors: Kundu, M. R.; Gopalswamy, N.; Saba, J. L. R.;
Schmelz, J. T. S.; Strong, K. T.
Bibliographic Code: 1987SoPh..114..273K
Abstract
The authors present a study of type III activity at meter-decameter
wavelengths in the preflare phase of the 1986 February 3 flare using
data obtained with the Clark Lake Multifrequency Radioheliograph. They
compare this activity with similar type III burst activity during the
impulsive phase and find that there is a displacement of burst sources
between the onset and end times of the activity. A comparison of this
displacement at three frequencies suggests that the type III emitting
electrons gain access progressively to diverging and different field
lines relative to the initial field lines. The energetics of the type
III emitting electrons are inferred from observations and compared with
those of the associated hard X-ray emitting electrons. The soft X-ray
data from SMM-XRP shows enhanced emission measure, density and
temperature in the region associated with the preflare type III
activity.
@--------------------------------------------------------------------
Title: Quiet sun and slowly varying component at meter and
decameter wavelengths
Authors: Lantos, P.; Alissandrakis, C. E.; Gergely, T.;
Kundu, M. R.
Bibliographic Code: 1987SoPh..112..325L
Abstract
Comparison of maps of the sun obtained over the period June 29 to July
8, 1982 at 169 MHz with the Nancay Radioheliograph and at 73.8, 50, and
30.9 MHz with the Clark Lake Radioheliograph shows that the slowly
varying component at meter and decameter wavelengths is not always
thermal emission. During the period under study weak noise storm
continua were the most frequent sources of slowly varying component at
169 and 73.8 MHz. Most filaments show no counterpart on the disk. A
streamer has been detected on the disk from 169 to 30.9 MHz with an
optimum observability at 50 MHz. The brightest source of the slowly
varying component from 73.8 to 30.9 MHz for most of the period was
located above an extended coronal hole in a region where a depression
was observed at 169 MHz. In favorable cases, electron densities can be
derived from the positions of noise storms and radio streamers; these
are in agreement with previous K-corona eclipse observations.
@--------------------------------------------------------------------
Title: Meterwave observations of a coronal hole
Authors: Wang, Z.; Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1987SoPh..111..419W
Abstract
Meter-wave maps showing a coronal hole at 30.9, 50.0, and 73.8 MHz are
presented using the Clark Lake Radioheliograph in October 1984. The
coronal hole seen against the disk at all three frequencies shows
interesting similarities to, and significant differences from, its
optical signatures in He I 10830 A spectroheliograms. Using the model of
coronal holes by Dulk et al. (1977), the electron density is derived
from the radio observations of the brightness temperature. The
discrepancy between the density value derived from the Skylab EUV data
and that computed from the present radio data is even larger than in
Dulk et al.'s comparison at similar and higher frequencies.
@--------------------------------------------------------------------
Title: Characteristics of shock-associated fast-drift
kilometric radio bursts
Authors: MacDowall, R. J.; Kundu, M. R.; Stone, R. G.
Bibliographic Code: 1987SoPh..111..397M
Abstract
The existence of a class of fast-drift, shock-associated (SA),
kilometric radio bursts which occur at the time of metric type II
emission and which are not entirely the kilometric continuation of
metric type III bursts has been reported previously (Cane et al., 1981).
In this paper, the authors establish unambiguous SA event criteria for
the purpose of statistically comparing SA events with conventional
kilometric type III bursts. They apply these criteria to all
long-duration, fast-drift bursts observed by the ISEE-3 spacecraft
during a 28-month interval and find that more than 70% of the events
satisfying the criteria are associated with the radio signatures of
coronal shocks. If a given event in this sample is associated with a
metric type II or type IV burst, it is 13 times more likely to satisfy
the SA criteria than an event associated only with metric type III
activity. Compared with conventional kilometric type III bursts, the
characteristics of these SA events are longer duration, higher maximum
intensity, and a larger number of components.
@--------------------------------------------------------------------
Title: Imaging observations of the evolution of
meter-decameter burst emission during a major flare
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1987SoPh..111..347G
Abstract
The results of a study of the evolution of the February 3, 1986 flare at
meter-decameter wavelengths are presented, using the two-dimensional
imaging observations made with the Clark Lake multifrequency
radioheliograph. The flare was complex and produced various types of
meter-decameter bursts. The preflare activity was observed in the form
of type III bursts some tens of minutes prior to the impulsive onset.
From the positional analysis of the preflare and impulsive phase type
III bursts and other measured characteristics, the characteristics of
energy release and possible magnetic field configurations in the
vicinity of the energy release region are discussed. From positional and
temporal studies of the flare continuum and type II burst in relation to
the microwave and hard X-ray emissions, the possible magnetic field
structures in which the accelerated particles are confined or along
which they propagate are discussed; a schematic model of the flaring
region is developed, based upon this study.
@--------------------------------------------------------------------
Title: Propagation of electrons emitting weak type III
bursts in coronal streamers
Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A.
Bibliographic Code: 1987SoPh..108..333G
Abstract
The observations of weak type III bursts at 73.8, 57.5, 50.0, and 38.5
MHz from Clark Lake Radio Observatory on four days are reported and
their characteristics are discussed. In addition to Clark Lake data, the
magnetogram and sunspot/active region data and the coronal streamer data
obtained by HAO's Coronagraph/Polarimeter aboard SMM satellite are used
to study the location of the burst sources with respect to the coronal
streamers emanating from active regions. It is shown that the bursts
occur within or close to the edge of dense coronal streamers implying
that the coronal streamers contain open magnetic field lines along which
the electrons generating the bursts propagate. The positional analysis
of the bursts is used to estimate the variation of coronal electron
density with radial distance.
@--------------------------------------------------------------------
Title: Meterwave observations of a coronal hole
Authors: Wang, Z.; Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1987sici.symp...24W
Abstract
Meter-wave maps are presented showing a coronal hole at 30.9, 50.0, and
73.8 MHz using the Clark Lake Radioheliograph in October 1984. The
coronal hole seen against the disk at all three frequencies shows
interesting similarities to, and significant differences from its
optical signatures in HeI lambda10830 spectroheliograms. The 73.8 MHz
coronal hole, when seen near disk center, appears to coincide with the
HeI footprint of the hole. At the lower frequencies, the emission comes
from higher levels of the corona, and the hole appears to be displaced,
probably due to the non-radial structure of the coronal hole. The
contrast of the hole relative to the quiet Sun is much greater than
reported previously for a coronal hole observed at 80 MHz. The higher
contrast is certainly real, due to the superior dynamic range,
sensitivity, and calibration of the Clark Lake instrument. Using a
coronal hole model, the electron density is derived from radio
observations of the brightness temperature. A very large discrepancy is
found between the derived density and that determined from Skylab EUV
observations of coronal holes. This discrepancy suggests that much of
the physics of coronal holes has yet to be elucidated.
@--------------------------------------------------------------------
Title: Two dimensional imaging observations of
meter-decameter bursts associated with the February
1986 flare activity
Authors: Gopalswamy, N.; Kundu, M. R.
Bibliographic Code: 1987sici.symp...16G
Abstract
An analysis is presented of the two dimensional imaging observations of
a flare observed on 3 Feb. l986 using the Clark Lake Multifrequency
Radioheliograph. The flare produced almost all types of Meter-decimeter
radio emission: enhanced storm radiation, type III/V bursts, II and IV
and flare continuum. The flare continuum had early (FCE) and late (FC
II) components and the type II occurred during the period between these
two components. Comparing the source positions of type III/V and FCE it
was found that these bursts must have occurred along adjacent open and
closed field lines, respectively. The positional analysis of type II and
FC II implies that the nonthermal electrons responsible for FC II need
not be accelerated by type II shock and this conclusion is further
supported by the close association of FC II with a microwave peak. Using
the positional and temporal analysis of all these bursts and the
associated hard X-ray and microwave emissions, a schematic model is
developed for the magnetic field configuration in the flaring region in
which the nonthermal particles responsible for these bursts are confined
or along which they propagate.
@--------------------------------------------------------------------
Title: The Effect of a Large Flare on the Solar Corona
Authors: Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.;
Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1987BAAS...19S1122S
Abstract
@--------------------------------------------------------------------
Title: Microwave Observations of the X-Flare of May 19,
1984
Authors: Schmahl, E. J.; Kundu, M. R.; Schmelz, J. T.;
Saba, J.; Strong, K. T.
Bibliographic Code: 1987BAAS...19R1122S
Abstract
@--------------------------------------------------------------------
Title: Coronal Bright Points in Microwaves: Their Optical
Associations and Emission Measures
Authors: Nitta, N.; Kundu, M. R.
Bibliographic Code: 1987BAAS...19.1122N
Abstract
@--------------------------------------------------------------------
Title: Simultaneous VLA observations of a flare at 6 and 20
centimeter wavelengths
Authors: Velusamy, T.; Kundu, M. R.; Schmahl, E. J.;
McCabe, M.
Bibliographic Code: 1987ApJ...319..984V
Abstract
Using the Very Large Array at 6 and 20 cm wavelengths, a May 15, 1980
solar flare was mapped. The 1B flare, as observed in H alpha at Mees
Solar Observatory, Maui, Hawaii, appeared as two sequential flares
occurring at different neutral lines. The peaks of the time profile at
20 cm were delayed with respect to the 6 cm counterparts, but they were
related to each other and to the H alpha activity. At 20 cm, precursor
activity occurred, and an oppositely polarized source an arcminute away
from the main burst may have triggered the flare. The main 20 cm
emission appeared to be displaced limbward from the 6 cm burst. If both
the 6 and 20 cm emission originated in the same system of loops, it is
inferred that the apparent lateral displacement was caused by a height
difference of 33,000 km in the sources of emission.
@--------------------------------------------------------------------
Title: A study of hard X-ray associated meter-decameter
bursts observed on December 19, 1979
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.;
Sawant, H. S.
Bibliographic Code: 1987STIN...8728486K
Abstract
The results of a study of the relationship of a complex meter-decameter
wavelength radio burst observed with the Clark Lake E-W and N-S
interferometers, with a hard X-ray burst observed with the X-ray
spectrometer aboard ISEE-3 are presented. The radio burst consisted of
several type III's, reverse drift type III's, a U burst, and type II and
type IV bursts. The X-ray emission was also complex. The radio as well
as hard X-ray emissions were observed before the flash phase of the
flare; they were not always associated and it is conjectured that this
may constitute evidence for acceleration of electrons high in the
corona. On the other hand, all components of the reverse drift burst
were associated with hard X-ray subpeaks, indicating multiple injection
of electron beams along field lines with different density gradients.
While the type II burst appeared to be related to the hard X-ray burst,
a detailed correspondence between individual features of the radio and
hard X-ray burst emissions could not be found. The type IV burst started
after all hard X-ray emissions ceased. Its source appeared to be a
magnetic arch, presumably containing energetic electrons responsible for
the gyrosynchrotron radiation of type IV.
@--------------------------------------------------------------------
Title: Coronal Bright Points at 6 and 20 cm Wavelengths
Authors: Kundu, M. R.; Schmahl, E. J.; Jackson, P. D.;
Fu, Q.-J.
Bibliographic Code: 1987BAAS...19..937K
Abstract
@--------------------------------------------------------------------
Title: Comparison of Large Scale Structures of the Corona
in White Light and Radio Wavelengths
Authors: Jackson, P. D.; Kundu, M. R.
Bibliographic Code: 1987BAAS...19..931J
Abstract
@--------------------------------------------------------------------
Title: Microwave Evidence for Large Scale Magnetic
Rearrangements Associated with a Filament Eruption
Authors: Schmahl, E. J.; Kundu, M. R.; Fu, Q.-J.
Bibliographic Code: 1987BAAS...19..925S
Abstract
@--------------------------------------------------------------------
Title: The plasma and magnetic field properties of coronal
loops observed at high spatial resolution
Authors: Webb, D. F.; Holman, G. D.; Davis, J. M.;
Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1987ApJ...315..716W
Abstract
Two data sets are analyzed in order to improve understanding of the
plasma and magnetic field properties of active region coronal loops.
Each set consists of coaligned, high spatial resolution soft X-ray,
microwave, and magnetogram images that are used to compare observations
of coronal loops and their feet in the photosphere and to constrain
possible microwave emission mechanisms. The loops are found to have
plasma parameters typical of quiescent active region loops. Each loop
has a compact microwave source with peak brightness temperature T(b) =
1-2.5 x 10 to the 6th K cospatial with or near the loop apex. No
complete loops are imaged in microwaves. The loop emission observed at
4.9 GHz is best described by fourth harmonic gyroresonance emission from
a dipole loop model, but with less field variation along the loop than
in the models of Holman and Kundu (1985).
@--------------------------------------------------------------------
Title: Very-large-array observations of a complex gradual
solar burst at 6 CM wavelength
Authors: Kundu, M. R.; McConnell, D.; White, S. M.;
Shevgaonkar, R. K.
Bibliographic Code: 1987A&A...176..131K
Abstract
The authors present a 6 cm VLA observation of a burst from a solar
active region. The burst shows a normal impulsive rise-and-fall
superimposed on a gradual component. The peak brightness temperature of
the burst remains relatively constant, and the flux variations are due
to changes in the source structure. It appears as though an arcade of
loops is gradually heated or filled with hot plasma. The burst is weakly
polarized but unipolar; the authors investigate the possible reasons for
this structure. Depolarization of optically thin emission due to twisted
magnetic fields within the source can produce significant
depolarization, but is probably not active in this event. Instead, it is
suggested that the flare emission is optically thick and that hot
overlying material preferentially absorbs one polarization.
@--------------------------------------------------------------------
Title: Correlated type III burst emission from distant
sources on the sun
Authors: Kundu, M. R.; Gopalswamy, N.
Bibliographic Code: 1987SoPh..112..133K
Abstract
The authors report the observation and interpretation of a correlated
type III burst emitted from distant sources on the Sun. The angular
separation between the distant sources is as large as 26arcmin or
≡106km. There was an active region ≡30°
behind the limb, and it is believed that the type III burst emission
originated from activity in this region. The implications of the
locations of the correlated sources with regard to the geometry of the
magnetic structures involved in the flare process are discussed.
@--------------------------------------------------------------------
Title: A type IV burst associated with a coronal streamer
disruption event
Authors: Kundu, M. R.
Bibliographic Code: 1987SoPh..111...53K
Abstract
A type IV burst was observed on February 17, 1985 with the Clark Lake
Radio Observatory multifrequency radioheliograph operating in the
frequency range 20 - 125 MHz. This burst was associated with a coronal
streamer disruption event. From two-dimensional images produced at 50
MHz, evidence is shown of a type II burst and a slow moving type IV
burst. The observations of the moving type IV burst suggests that a
plasmoid containing energetic electrons can result from the disruption
of a coronal streamer.
@--------------------------------------------------------------------
Title: Large-scale structure of the sun's corona from radio
observations using the Clark Lake Radioheliograph
Authors: Kundu, M. R.; Gergely, T. E.; Schmahl, E. J.;
Szabo, A.; Loiacono, R.
Bibliographic Code: 1987SoPh..108..113K
Abstract
Meterwave maps of the solar corona made with the Clark Lake
Radioheliograph at 30.9, 50, and 73.8 MHz for one solar rotation are
presented. They are compared and contrasted with optical data: 10,830 A
maps, white-light coronagraph images (SOLWIND and Mauna Loa K
coronameter), and forbidden line scans. Most of the sources in the radio
maps persist for two days or more, and appear to rotate approximately
with the solar rate. A coronal hole seen against the disk at all three
frequencies shows interesting similarities and significant differences
with the optical signatures of the hole. Elongated features of the 50
MHz corona correspond rather well to the azimuthal position of white
light streamers seen in SOLWIND images. Synoptic charts made from the
radio maps show overall similarities to synoptic charts constructed from
(limb) coronagraph data. Some of the differences may result from the
different weightings given by the radio and optical data to density and
temperature, or by the different sensitivities to nonradial geometries.
It is shown that the combined use of meter wave and optical images
provides considerable new insights into the three-dimensional structure
of the low to middle corona.
@--------------------------------------------------------------------
Title: Coronal bright points at 6 CM wavelength
Authors: Fu, Q.; Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1987SoPh..108...99F
Abstract
The results of the first observations of solar coronal bright points at
6 cm wavelength using the Very Large Array (VLA), with a spatial
resolution of about 1.2 arcsec, are reported. The maximum brightness
temperature of the sources observed is about 30,000 K with a mean value
of about 10,000 K (above the quiet sun value). The lifetime of most
sources is between 5 and 20 min. The average diameter of the sources is
about 5-15 arcsec. The sources are Gaussian-like near the footpoint of
miniature loops and they appear in groups. The observations indicate
that significant fluctuations in the brightness temperature (sometimes
quasi-periodic) and in the spatial extents of these sources can occur
over periods of a few minutes.
@--------------------------------------------------------------------
Title: Clark Lake microbursts - On a lower limit to type
III burst brightness temperatures
Authors: White, S. M.; Kundu, M. R.; Szabo, A.
Bibliographic Code: 1987SoPh..107..135W
Abstract
Further observations of solar microbursts by the Clark Lake
radioheliograph are reported. The microbursts have properties consistent
with weak type III bursts, with the implication that type III's can have
brightness temperatures as low as 1 million K. The importance of this
result is explored. A single model to explain the stronger type III
bursts and the weaker microbursts is sought. It is shown that none of
the models for stabilizing the strongest type III electron streams can
explain the observed microbursts: these models have threshold levels of
Langmuir waves which imply emission (due to spontaneous scattering off
ions) with brightness temperatures in excess of those observed. It
appears that either some vital physics is still missing from models for
type III bursts, or that microbursts should have properties
significantly different from those of type III bursts. In the latter
case further observations should allow important tests of type III
models.
@--------------------------------------------------------------------
Title: Microwave observations of the flare stars UV Ceti,
AT Microscopii, and AU Microscopii
Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.;
Melozzi, M.
Bibliographic Code: 1987ApJ...312..822K
Abstract
The results of observations of three red dwarf flare star systems, UV
Ceti, AT Mic, and AU Mic, made in February and March of 1985, are
reported. Flaring was detected from all three systems, and quiescent
emission from UV Cet and AU Mic. Models for the quiescent
microwave-emitting corona of UV Cet are discussed. The gravitational
scale height in current models is similar to or larger than the height
of the corona, which is a striking difference from the case of the solar
corona and confirms that magnetic structures are required to confine the
radio-emitting corona. The role of precipitation into the chromosphere
of the energetic particles in such a corona is explored, and it is shown
that for plausible parameters it may be the dominant energy loss
mechanism.
@--------------------------------------------------------------------
Title: 6 and 20 cm wavelength observations of coronal
bright points
Authors: Kundu, M. R.; Schmahl, E. J.; Fu, Q. J.
Bibliographic Code: 1987SoPh..113..305K
Abstract
@--------------------------------------------------------------------
Title: Multiwavelength Microwave Observations of Solar
Active Regions and Flares
Authors: Kundu, M. R.
Bibliographic Code: 1987sman.work...25K
Abstract
A preflare active region was studied using the Very Large Array (VLA) at
2, 6 and 20 cm. The author also carried out simultaneous observations of
a microwave burst at 2 and 6 cm wavelengths with the VLA.
@--------------------------------------------------------------------
Title: A VLA Survey of dMe Flare Stars
Authors: Jackson, P. D.; Kundu, M. R.; White, S. M.
Bibliographic Code: 1987LNP...291..103J
Abstract
A survey is underway, which uses the VLA at wavelengths of 6 and 20 cm,
to search for radio emission from all dMe flare stars within about 10
parcsecs of the Sun, and which have not yet been widely observed at
radio wavelengths. Results so far, based on a total observing time of
about one hour each during July 1986 have yielded detections from 9 of
the 27 stellar systems in the program.
@--------------------------------------------------------------------
Title: Microwave Observations of Red Dwarf Flare Stars
Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.
Bibliographic Code: 1987LNP...291..100K
Abstract
Observations of AD Leo, EQ Peg AB, L726-8AB (B = UV Ceti), Wolf 630AB,
YY Gem and YZ CMi were made on March 22, 1985 in the 6 and 20 cm
wavelength bands using the Very Large Array with hybrid A/B
configuration.
@--------------------------------------------------------------------
Title: VLA observations of coronal bright points at 6 and
20 CM wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1986NASCP2442..349K
Abstract
Prior to and during the Spacelab-2 operation, observations were made at
6 and 20 cm of solar coronal bright points, using the Very Large Array
(VLA) in the C-configuration. The ultraviolet coverage ranged from 200
to 18,000 wavelengths. The maps were convolved with beams of 18 x 18
inches at 20 km and 4 x 4 inches at 6 cm. Only the preliminary results
from July 15 and July 31, 1985 observations.
@--------------------------------------------------------------------
Title: Three dimensional structures of solar active regions
Authors: Kundu, M. R.
Bibliographic Code: 1986NASCP2442..291K
Abstract
Three dimensional structure of an active region is determined from
observations with the Very Large Array (VLA) at 2, 6, and 20 cm. This
region exhibits a single magnetic loop of length approx. 10 to the 10th
power cm. The 2 cm radiation is mostly thermal bremsstrahlung and
originates from the footpoints of the loop. The 6 and 20 cm radiation is
dominated by the low harmonic gyroresonance radiation and originates
from the upper portion of the legs or the top of the loop. The loop
broadens toward the apex. The top of the loop is not found to be the
hottest point, but two temperature maxima on either side of the loop
apex are observed, which is consistent with the model proposed for long
loops. From 2 and 6 cm observations it can be concluded that the
electron density and temperature cannot be uniform in a plane
perpendicular to the axis of the loop; the density should decrease away
from the axis of the loop.
@--------------------------------------------------------------------
Title: Large scale structure of the sun's radio corona
Authors: Kundu, M. R.
Bibliographic Code: 1986NASCP2442..253K
Abstract
The author presents results of studies of large scale structures of the
corona at long radio wavelengths, using data obtained with the
multifrequency radioheliograph of the Clark Lake Radio Observatory. He
shows that features corresponding to coronal streamers and coronal holes
are readily apparent in the Clark Lake maps.
@--------------------------------------------------------------------
Title: Large scale structure of the corona
Authors: Kundu, M. R.
Bibliographic Code: 1986NASCP2442..249K
Abstract
This is an introduction to this section of the proceedings. In this
section is a brief description of some radio results obtained with
meter-decameter radioheliograph. An optical study based upon synoptic
data of polarized brightness (pB), H alpha line filtergrams and large
scale B-fields is presented. This is followed by two papers on the
interpretation of coronal mass ejection (CME) and modeling of three
dimensional coronas.
@--------------------------------------------------------------------
Title: VLA observations of solar filaments at 6 and 20 CM
wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1986NASCP2442..117K
Abstract
Using the Very Large Array the author observed several solar filaments
at 1.5 and 5 GHz. The brightness temperatures of the filaments are 4 -
5×104K at 20 cm and 1.5 - 1.6×104K at
6 cm. The maximum temperature depressions appear to be associated with
Halpha filaments. Comparison with He 10830 Å spectroheliogram
shows that 20 cm temperature depressions correspond to the regions of
reduced intensity in the He 10830 Å around filaments, which
correspond to coronal cavities. The author studied the temperature and
density structure of the transition sheath between the filament and the
surrounding corona assuming that the energy radiated away is balanced by
the energy conducted from the corona. He found that the observations can
be better explained by a model having a pressure gradient in the
transition sheath around the filament.
@--------------------------------------------------------------------
Title: Impulsive Phase Observations and Their
Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.;
Dulk, G. A.; Emslie, A. G.; Enome, S.;
Gabriel, A. H.; Kundu, M. R.; Melrose, D.;
Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.;
Rieger, E.; Tanaka, K.; Zirin, H.
Bibliographic Code: 1986epos.conf..3.4C
Abstract
@--------------------------------------------------------------------
Title: Phenomena Associated with Mildly Relativistic
Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.;
Murphy, R. J.; Allisandrakis, C.; Bai, T.;
Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.;
Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.;
MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.;
Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.;
Tsuneta, S.; van Hoven, G.
Bibliographic Code: 1986epos.conf..2.2V
Abstract
@--------------------------------------------------------------------
Title: A study of solar filaments from high resolution
microwave observations
Authors: Kundu, M. R.; Melozzi, M.; Shevgaonkar, R. K.
Bibliographic Code: 1986A&A...167..166K
Abstract
Using the Very Large Array the authors have observed several solar
filaments at 1.5 and 5 GHz. The brightness temperatures of the filaments
are 4 - 5×104K at 20 cm and 1.5 -
1.6×104K at 6 cm. The maximum temperature depressions
appear to be associated with Halpha filaments. Comparison with He
10830 Å spectroheliogram shows that 20 cm temperature depressions
correspond to the region of reduced intensity in the He 10830 Å
around filaments, which correspond to coronal cavities. The authors have
studied the temperature and density structure of the transition sheath
between the filament and the surrounding corona assuming that the energy
radiated away is balanced by the energy conducted from the corona. They
find that the observations can be better explained by a model having a
pressure gradient in the transition sheath around the filament.
@--------------------------------------------------------------------
Title: Book-Review - Solar Terrestrial Physics
Authors: Kundu, M. R.; Biswas, S.; Reddy, B. M.;
Samadurai, S.; Somov, B. V.
Bibliographic Code: 1986SSRv...44..403K
Abstract
@--------------------------------------------------------------------
Title: Coronal Activity at Meter-Decameter Wavelengths:
Clark Lake Observations
Authors: Schmahl, E. J.; Kundu, M. R.; Szabo, A.;
Gergely, T. E.; Howard, R.
Bibliographic Code: 1986BAAS...18R.900S
Abstract
@--------------------------------------------------------------------
Title: Propagation of Weak Type III Burst Electrons in
Dense Coronal Streamers
Authors: Gopalswamy, N.; Kundu, M. R.; Szabo, A.
Bibliographic Code: 1986BAAS...18R.900G
Abstract
@--------------------------------------------------------------------
Title: Microwave Observations of Red Dwarf Flare Stars
Authors: Kundu, M. R.; Jackson, P. D.; White, S. M.
Bibliographic Code: 1986BAAS...18..984K
Abstract
@--------------------------------------------------------------------
Title: Simultaneous VLA and Hard X-Ray Observations of a
Large Flare on 1981 November 14
Authors: Dennis, B. R.; Kundu, M. R.; Melozzi, M.
Bibliographic Code: 1986BAAS...18..965D
Abstract
@--------------------------------------------------------------------
Title: A VLA Survey of dMe Flare Stars
Authors: Jackson, P. D.; Kundu, M. R.; White, S. M.
Bibliographic Code: 1986BAAS...18..913J
Abstract
@--------------------------------------------------------------------
Title: Solar microbursts at meter-dekameter wavelengths
Authors: Kundu, M. R.; Gergely, T. E.; Szabo, A.;
Loiacono, R.; White, S. M.
Bibliographic Code: 1986ApJ...308..436K
Abstract
Microbursts are low-brightness-temperature bursts observed by the Clark
Lake radioheliograph. The bursts occur several times per hour during
quiet-sun periods and are seen at the observing frequencies from 30 to
70 MHz. They are stationary at a given frequency, have short rise times
and durations of 2-10 s. Here, observations of the bursts are presented
and interpretated in terms of plasma emission. The burst properties
suggest that they are weak type III bursts. The observations imply that
energy releases on the sun continue to be impulsive, with nonthermal
electron distributions, for small releases of energy. The relation of
the bursts to type III bursts and hard X-ray bursts is discussed.
@--------------------------------------------------------------------
Title: Solar coronal bright points observed with the VLA
Authors: Habbal, S. R.; Ronan, R. S.; Withbroe, G. L.;
Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1986ApJ...306..740H
Abstract
The first observations of solar coronal bright points made at 20-cm
wavelength with the VLA are reported. The brightness temperature of the
sources observed varies between 1 and 5 x 10 to the 5th K. The
observations indicate that significant fluctuations in the brightness
temperature as well as in the spatial extent of these sources can occur
over a few minutes. These fluctuations are shown to be due to density
and temperature fluctuations at transition region heights combined with
either plasma motions along magnetic field lines or changes in magnetic
field topology, or both.
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics
Authors: Kundu, M. R.; Holman, G. C.; Somov, B. V.
Bibliographic Code: 1986SSRv...44..187K
Abstract
@--------------------------------------------------------------------
Title: A new microwave/X-ray diagnostic for the thermal
phase of solar flares
Authors: Schmahl, E. J.; Kundu, M. R.; Erskine, F. T.
Bibliographic Code: 1986SoPh..105...87S
Abstract
Ten solar bursts were observed during the thermal phase using the
Haystack radio telescope at 22 GHz. It is shown that these high
frequency flux observations, when compared with soft X-ray band fluxes,
give useful information about the temperature profile in the flare
loops. The microwave and X-ray band fluxes provide determinations of the
maximum loop temperature, the total emission measure, and the index
delta of the differential emission measure. The special case of an
isothermal loop has been considered previously by Thomas et al. (1985),
and the present paper confirms their diagnostic calculations for the
GOES X-ray bands, but finds that the observed flare loops departed
significantly from the isothermal regime. The present results (delta =
1-3.5) imply that, during the late phases of flares, condensation
cooling competes with radiative cooling. Further, the results appear to
be in good agreement with previous deductions from XUV rocket spectra.
@--------------------------------------------------------------------
Title: Clark Lake microbursts: on a lower limit to type III
burst brightnesstemperatures.
Authors: White, S. M.; Kundu, M. R.; Szabo, A.
Bibliographic Code: 1986SoPh..107..135W
Abstract
Further observations of solar microbursts by the Clark Lake
radioheliograph are reported. The microbursts have properties consistent
with weak type III bursts, with the implication that type III's can have
brightness temperatures as low as 106K. The authors explore
the importance of this result. A single model to explain the stronger
type III bursts and the weaker microbursts is sought. The authors show
that none of the models for stabilizing the strongest type III electron
streams can explain the observed microbursts: these models have
threshold levels of Langmuir waves which imply emission (due to
spontaneous scattering off ions) with brightness temperatures in excess
of those observed. It appears that either some vital physics is still
missing from models for type III bursts, or that microbursts should have
properties significantly different from those of type III bursts. In the
latter case further observations should allow important tests of type
III models.
@--------------------------------------------------------------------
Title: Decimeter continuum radio emission from a post-flare
loop
Authors: Kundu, M. R.
Bibliographic Code: 1986SoPh..104..223K
Abstract
It is shown how radio observations permitted the estimation of magnetic
fields in the postflare loop associated with the May 19, 1979
long-lasting burst. The strongest 20-cm burst source is associated with
H-alpha brightening at 20:41 UT. A comparison of spatially-resolved
microwave and soft X-ray emission connected with the flare loop event
showed that, at the time of maximum 20-cm flux from the source
associated spatially with the declining X-ray flare, as much as one-half
of the 20-cm flux could be thermal bremsstrahlung from the X-ray
postflare groups. It is suggested that this 20-cm burst emission is
produced either by a thermal free-free process or by thermal/nonthermal
gyroradiation.
@--------------------------------------------------------------------
Title: High-Spatial-Resolution Microwave and Soft X-ray
Observations as Diagnostics of Solar Magnetic Loops
Authors: Holman, G. D.; Webb, D. F.; Davis, J. M.;
Kundu, M. R.
Bibliographic Code: 1986BAAS...18..677H
Abstract
@--------------------------------------------------------------------
Title: A study of hard X-ray associated meter-decameter
bursts observed on December 19, 1979
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.;
Sawant, H. S.
Bibliographic Code: 1986SoPh..103..153K
Abstract
The results of a study of the relationship of a complex meter-decameter
wavelength radio burst observed with the Clark Lake E-W and N-S
interferometers, with a hard X-ray burst observed with the X-ray
spectrometer aboard ISEE-3 are presented. The radio burst consisted of
several type III's, reverse drift type III's, a U burst, and type II and
type IV bursts. The X-ray emission was also complex. The radio as well
as hard X-ray emissions were observed before the flash phase of the
flare; they were not always associated and it is conjectured that this
may constitute evidence for acceleration of electrons high in the
corona. On the other hand, all components of the reverse drift burst
were associated with hard X-ray subpeaks, indicating multiple injection
of electron beams along field lines with different density gradients.
While the type II burst appeared to be related to the hard X-ray burst,
a detailed correspondence between individual features of the radio and
hard X-ray burst emissions could not be found. The type IV burst started
after all hard X-ray emissions ceased. Its source appeared to be a
magnetic arch, presumably containing energetic electrons reponsible for
the gyrosynchrotron radiation of type IV.
@--------------------------------------------------------------------
Title: High Spatial Resolution Microwave Observations of
Solar Flares
Authors: Kundu, M. R.
Bibliographic Code: 1986spps.book..159K
Abstract
@--------------------------------------------------------------------
Title: Solar-terrestrial physics. Proceedings of the second
Indo-US workshopon solar-terrestrial physics, held
at New Delhi, India, 30 January - 3 February 1984.
Authors: Kundu, M. R.; Biswas, S.; Reddy, B. M.;
Samadurai, S.
Bibliographic Code: 1986spps.book.....K
Abstract
@--------------------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.;
Dulk, G. A.; Emslie, A. G.; Enome, S.;
Gabriel, A. H.; Kundu, M. R.; Melrose, D.;
Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.;
Rieger, E.; Tanaka, K.; Zirin, H.
Bibliographic Code: 1986NASCP2439....3C
Abstract
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard X-ray
and microwave morphology, combined soft and hard X-ray spectra, iron
Kalpha emission, ultraviolet and hard X-ray emission, white light
emission, Halpha emission. 3. Theoretical studies of transport
processes: electron beams and reverse currents, proton transport,
radiative energy transport by amplified decimetric waves. 4. Summary.
@--------------------------------------------------------------------
Title: Particle acceleration.
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.;
Murphy, R. J.; Allisandrakis, C.; Bai, T.;
Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.;
Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.;
MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.;
Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.;
Tsuneta, S.; van Hoven, G.
Bibliographic Code: 1986NASCP2439....2V
Abstract
Contents: 1. Introduction. 2. Phenomena associated with
mildly-relativistic electrons: soft and hard X-ray source structure,
location and development, microwave source structure, location and
development, time structures and time delays in radio and hard X-rays,
microwave rich flares, decimetric - metric observations and comparison
with X-ray observations, discussion of models for X-ray and microwave
emission. 3. Phenomena associated with ions and relativistic electrons:
gamma-ray observations, neutron observations, implications of gamma-ray
and neutron observations, interplanetary charged-particle observations,
acceleration mechanisms. 4. Mechanisms for particle acceleration in
flares: particle acceleration in reconnecting magnetic fields, electron
acceleration along the magnetic field with sub-Dreicer electric fields,
lower hybrid waves, Fermi acceleration and MHD turbulence, shock
acceleration, acceleration of electrons by intense radio waves,
preferential acceleration of heavy ions. 5. Achievements - outstanding
questions.
@--------------------------------------------------------------------
Title: Microwave Observations of Flare Stars UV Ceti, AT
Mic, and AU Mic
Authors: Kundu, M. R.; Jackson, P. D.; Melozzi, M.;
White, S. M.
Bibliographic Code: 1986LNP...254..284K
Abstract
@--------------------------------------------------------------------
Title: EXOSAT Detection of a Very Large Flare on EQ Peg
Authors: Pallavicini, R.; Kundu, M. R.; Jackson, P. D.
Bibliographic Code: 1986LNP...254..225P
Abstract
During a program of coordinated EXOSAT and VLA observations of flare
stars, the authors have detected a large X-ray burst on EQ Peg
(dM4e+dM6e). Although flares are common at all wavelengths in classical
flare stars, the high intensity, long duration and spectral
characteristics of the detected event make it rather exceptional and
worth an early report. A preliminary analysis of the X-ray observations
is presented.
@--------------------------------------------------------------------
Title: Possible evidence for beaming in flares from
microwave and hard X-ray imaging and spectra
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
Bibliographic Code: 1986lasf.conf..396S
Abstract
The magnetic field strength and number of burst-producing energetic
electrons are presently deduced for the impulsive phase of a solar flare
at microwave wavelengths, with the VLA, and hard X-rays, with the SMM
Hard X-ray Burst Spectrometer. The combined data indicate that the
number of microwave-emitting electrons is at least three orders of
magnitude smaller than the number of thick target electrons producing
the hard X-rays; this is suggested to be due to the high beaming and
inefficient radiation of gyrosynchrotron emission by comparison with
isotropically distributed electrons.
@--------------------------------------------------------------------
Title: Coronal activity at radio wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1986HiA.....7..725K
Abstract
The author describes the multifrequency radioheliograph of the Clark
Lake Radio Observatory. Its use for studies of large scale structures of
the corona at long radio wavelengths is discussed. The author shows that
features corresponding to coronal streamers and coronal holes are
readily apparent in the Clark Lake maps. The author also presents
results on studies of microbursts at meter-decameter wavelengths.
@--------------------------------------------------------------------
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.;
Dulk, G. A.; Emslie, A. G.; Enome, S.;
Gabriel, A. H.; Kundu, M. R.; Melrose, D.;
Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.;
Rieger, E.; Tanaka, K.; Zirin, H.
Bibliographic Code: 1986epos.conf.3.34C
Abstract
@--------------------------------------------------------------------
Title: Mechanisms for Particle Accleration in Flares
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.;
Murphy, R. J.; Allisandrakis, C.; Bai, T.;
Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.;
Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.;
MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.;
Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.;
Tsuneta, S.; van Hoven, G.
Bibliographic Code: 1986epos.conf.2.42V
Abstract
@--------------------------------------------------------------------
Title: Phenomena Associated with Ions and Relativistic
Electrons
Authors: Vlahos, L.; Machado, M. E.; Ramaty, R.;
Murphy, R. J.; Allisandrakis, C.; Bai, T.;
Batchelor, D.; Benz, A. O.; Chupp, E.; Ellison, D.;
Evenson, P.; Forrest, D. J.; Holman, G.; Kane, S. R.;
Kaufmann, P.; Kundu, M. R.; Lin, R. P.;
MacKinnon, A.; Nakajima, H.; Pesses, M.; Pick, M.;
Ryan, J.; Schwartz, R. A.; Smith, D. F.; Trottet, G.;
Tsuneta, S.; van Hoven, G.
Bibliographic Code: 1986epos.conf.2.30V
Abstract
@--------------------------------------------------------------------
Title: Microbursts observed at Clark Lake
Authors: White, S. M.; Kundu, M. R.; Gergely, T. E.
Bibliographic Code: 1986AdSpR...6Q.285W
Abstract
Microbursts are low brightness temperature burst observed by the Clark
Lake radioheliograph. The bursts are seen at the observing frequencies
from 30 MHz to 70 MHz, are stationary at a given frequency, and have
short rise times and durations of 2 - 10 seconds. We present
observations of the bursts, and show that their properties imply that
they are weak type III bursts. However, we also show that none of the
theories invoked to explain strong type III bursts can accomodate such
weak bursts. We expect that important differences in the properties of
microbursts and the stronger type III's will be found, and will be
important in understanding the propagation of electron streams in the
corona.
@--------------------------------------------------------------------
Title: Shock waves and coronal transients - The event of
1980 April 17
Authors: Gary, D. E.; Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1986AdSpR...6..311G
Abstract
The coronal mass ejection (CME) event of 1980 April 17 was observed with
the SMM coronograph, and an accompanying Type II (shock wave related)
burst was observed simultaneously with the Culgoora and Clark Lake
radioheliographs. The method of analysis of the combined radio
observations is presented. Although the radio positions were affected by
severe ionospheric refraction, the combined radio observations allow a
useful reduction in the range of possible positions of the 80 MHz source
when the 43 MHz source is required to lie within the range of position
angles of the CME. The positions of the 80 MHz radio sources under this
assumption are compared with the positions of the CME loop.
@--------------------------------------------------------------------
Title: Impulsive energy release in solar flares - A summary
Authors: Kundu, M. R.
Bibliographic Code: 1986AdSpR...6..207K
Abstract
Discoveries in solar physics made during the SMM-SMY-SMA period are
highlighted, with special reference to impulsive energy release in solar
flares. Major discoveries include observational evidence for magnetic
reconnection and its theoretical interpretation, chromospheric
evaporation to explain the simultaneous blue shift of X-ray lines and
red shift of H-alpha, simultaneous production of high energy (Mev)
electrons and protons, and their acceleration by Fermi shock
acceleration up to 100 Mev energies. They also include evidence for a
new acceleration process explaining the electron-deficient very hard ion
spectrum (greater than 1000 Mev) in the extended emission phase of the
large June 3, 1982 flare.
@--------------------------------------------------------------------
Title: Simultaneous imaging and spectral observations in
microwaves and hard X-rays of the impulsive phase of
a solar limb flare
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
Bibliographic Code: 1986AdSpR...6..143S
Abstract
Observations of the impulsive phase of a solar flare at microwave
wavelengths and in hard X-rays are used to deduce the strength of the
magnetic field and the number of energetic electrons producing the
burst. The microwave observations, using the VLA at 6 cm, had spatial
resolution of 8 x 8 arcsec, close to the resolution of the Hard X-ray
Imaging Spectrometer on SMM which also imaged this flare. The Hard X-ray
Burst Spectrometer determined the spectrum of the burst in the range
25-512 keV, and several patrol telescopes recorded the microwave time
profile at frequencies from 2.8 to 19.6 GHz. The combined data show that
the derived number of microwave-emitting electrons is at least three
orders of magnitude fewer than the number of thick target electrons
producing the hard X-rays. It is proposed that the fast electrons are
highly beamed and radiate gyrosynchrotron emission less efficiently than
isotropically distributed electrons.
@--------------------------------------------------------------------
Title: EXOSAT observations of quiescent and flaring
emission from active late-type stars
Authors: Pallavicini, R.; Monsignori-Fossi, B. C.;
Landini, M.; Kundu, M. R.; Lang, K. R.
Bibliographic Code: 1986AdSpR...6..125P
Abstract
The authors present the highlights of several guest investigator
programs carried out with the EXOSAT satellite. They discuss quiescent
as well as flaring emission from normal F to M dwarfs, from dMe flare
stars and from RS CVn binaries.
@--------------------------------------------------------------------
Title: Microwave observations of red dwarf flare stars
Authors: Kundu, M. R.; White, S. M.; Jackson, P. D.
Bibliographic Code: 1986AdSpR...6..117K
Abstract
Some recent observations of red dwarf flare stars are discussed. When
observed over periods of about 8 hours, each of 4 flare star systems
displayed at least one major flare at 20 cm. Quiescent emission at 6 cm
was seen from UV Ceti and EQ Peg A, but flares were much less frequent
at 6 cm than at 20 cm. Earlier observations of quiescent emission from
UV Ceti are also summarized. Observations of highly polarized flares
with brightness temperatures in excess of 10 to the 10th K appear to be
common on red dwarf stars. Narrowband flares which strengthen the
argument that a coherent emission mechanism is involved in these flares
have been found. One of those narrowband flares allows for the placement
of severe constraints on conditions in the flare source, and if the
flare is cyclotron maser emission it seems unlikely that magnetic
reconnection is involved in the flare.
@--------------------------------------------------------------------
Title: A high spatial resolution study of microwave flare
precursors
Authors: Kundu, M. R.
Bibliographic Code: 1986AdSpR...6...93K
Abstract
The author provides several examples of preflare changes from VLA high
resolution microwave data, which show that in general the active region
increases in intensity and polarization over a period of several tens of
minutes prior to the onset of a flare in that region. However, this
phenomenon by itself does not appear to be sufficient to trigger a
flare. The author shows that a few minutes (⪅10 min) just before the
flare onset something else happens, usually in the form of one of the
following three features: (1) sudden change of polarization of the
flaring region; (2) change of orientation of the neutral plane
separating one polarity from another in a bipolar region; and (3)
appearance of new sources in the immediate vicinity of some pre-existing
structure of the active region. All three features are consistent with
the emergence of new flux, which interacts with a pre-existing region to
form a neutral or current sheet. The formation of the latter is
ultimately responsible for triggering the onset of a flare.
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics - I.A.U. SYMP.107
Authors: Kundu, M. R.; Holman, G. D.; Roberts, B.
Bibliographic Code: 1985Obs...105..240K
Abstract
@--------------------------------------------------------------------
Title: Microwave imaging of a solar limb flare - Comparison
of spectra and spatial geometry with hard X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Dennis, B. R.
Bibliographic Code: 1985ApJ...299.1017S
Abstract
A solar limb flare was mapped using the Very Large Array (VLA) together
with hard X-ray (HXR) spectral and spatial observations of the Solar
Maximum Mission satellite. Microwave flux records from 2.8 to 19.6 GHz
were instrumental in determining the burst spectrum, which has a maximum
at 10 GHz. The flux spectrum and area of the burst sources were used to
determine the number of electrons producing gyrosynchrotron emission,
magnetic field strength, and the energy distribution of
gyrosynchrotron-emitting electrons. Applying the thick target model to
the HXR spectrum, the number of high energy electrons responsible for
the X-ray bursts was found to be 10 to the 36th, and the electron energy
distribution was approximately E exp -5, significantly different from
the parameters derived from the microwave observations. The HXR imaging
observations exhibit some similiarities in size and structure o the
first two burst sources mapped with the VLA. However, during the initial
burst, the HXR source was single and lower in the corona than the double
6 cm source. The observations are explained in terms of a single loop
with an isotropic high-energy electron distribution which produced the
microwaves, and a larger beamed component which produced the HXR at the
feet of the loop.
@--------------------------------------------------------------------
Title: Simultaneous observations of hard X-ray and
microwave burst sources in a limb flare
Authors: Takakura, T.; Kundu, M. R.; McConnell, D.; Ohki, K.
Bibliographic Code: 1985ApJ...298..431T
Abstract
Associated with a flare that occurred just behind the west solar limb on
1981 August 3, a hard X-ray source (20 - 30 keV) and a microwave source
at 5 GHz were observed simultaneously with the Hinotori spacecraft and
the VLA. Both sources were located in the corona. The height of the
centroid above the west limb was 15arcsec (104km) for the
hard X-ray source and 54arcsec (4×104km) for the radio
source. The sources are believed to be located near the tops of two
independent coronal arcades or loops, one low and the other high, rather
than at two different heights of a common arcade or loop.
@--------------------------------------------------------------------
Title: High spatial resolution microwave observations of
the sun
Authors: Kundu, M. R.
Bibliographic Code: 1985SoPh..100..491K
Abstract
Some results are given that have been obtained at Maryland, based on
observations with the Westerbork Synthesis Radio Telescope (WSRT) and
the Very Large Array (VLA) on the quiet sun (supergranulation network
and limb profile), active regions (sunspot-associated regions and
coronal loops), and flaring regions. Topics covered include:
observations of filaments; microwave active regions; determination of
magnetic fields in the low corona; radio observations of coronal loops;
and observations of flares with the VLA.
@--------------------------------------------------------------------
Title: Microwave emission from late-type dwarf stars UV
Ceti and YZ Canis Minoris
Authors: Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1985ApJ...297..644K
Abstract
Simultaneous high-resolution observations of two late-type dwarf stars,
UV Cet and YZ CMi, at 6 and 20 cm are presented. These observations put
sufficient constraints on existing interpretations to conclude that the
quiescent microwave emission from these stars is due to gyrosynchrotron
radiation of nonthermal electrons having a power-law energy
distribution. From the lifetime of 1 hr of the nonthermal particles
against radiation and collision losses, a magnetic field of a few
thousand gauss on the photosphere of these stars is estimated. The
observations indicate that the ambient density in the coronae of YZ CMi
is an order of magnitude higher than that of UV Cet.
@--------------------------------------------------------------------
Title: The diameter of the sun at decameter wavelengths
Authors: Gergely, T. E.; Gross, B. D.; Kundu, M. R.
Bibliographic Code: 1985SoPh...99..323G
Abstract
Using observations obtained with the Clark Lake radioheliogrpah, the
diameter of the sun was determiend in the decameter wavelength range.
Both equatorial and polar diameters increase with decreasing frequency,
as D = Af exp alpha. The eccentricity of the brightness distribution
appears to remain constant in the frequency range 30-74 MHz, in good
agreement with the optical results in a corresponding height range. The
smaller size of the polar diameter is attributed to coronal holes
covering the poles during the period of the observations, while
streamers were observed at the equator most of the time.
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.
Bibliographic Code: 1985S&T....70..134K
Abstract
@--------------------------------------------------------------------
Title: VLA observations of a radio plage at centimeter
wavelengths
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1985SoPh...98..119S
Abstract
VLA observations of a solar plage region at 6 and 20 cm wavelengths are
presented. The high frequency 6 cm emission correlates well with the
associated sunspots, whereas 20 cm emission shows good correlation with
the Halpha plage. Large temperature variations over a period of one
day are observed in the plage associated component without any
significant changes in the sunspots. The dominant emission mechanisms at
6 and 20 cm are found to be gyroresonance radiation and bremsstrahlung
respectively. It is concluded that the coronal condensation above the
chromospheric Halpha plage has an electron density of
≡5×109cm-3 and it extends to a height
of ≡5×104km.
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.
Bibliographic Code: 1985Sci...229...46K
Abstract
@--------------------------------------------------------------------
Title: Summary of the Current and Future Problems in Radio
Stars
Authors: Kundu, M. R.; Hjellming, R. M.
Bibliographic Code: 1985ASSL..116..397K
Abstract
@--------------------------------------------------------------------
Title: Microwave Emission from Late Type Dwarf Stars UV
Ceti and YZ CMi
Authors: Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1985ASSL..116..229K
Abstract
The authors present simultaneous VLA observations of two late type dwarf
stars UV Ceti and YZ CMi at 6 and 20 cm. Multiwavelength observations
put sufficient constraints on existing interpretations of quiescent
radio emission from these stars. They found that the microwave emission
is due to gyro-synchrotron radiation of nonthermal electrons having a
power law energy distribution. This emission originates from a source
whose size is 2 - 3 times larger than the star. The authors estimate a
magnetic field of ≡140 G and a density of
⪅2×108cm-3 in the microwave source.
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.; Kleczek, J.
Bibliographic Code: 1985Ap&SS.113..424K
Abstract
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.; Achterberg, A.
Bibliographic Code: 1985SSRv...41..212K
Abstract
@--------------------------------------------------------------------
Title: Simultaneous microwave observations of solar flares
at 6 and 20 CM wavelengths using the VLA
Authors: Melozzi, M.; Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1985SoPh...97..345M
Abstract
Using the Very Large Array, solar burst observations have been carried
out simultaneously at 6 and 20 cm. Structural changes and preheating
have been observed in the flaring regions on time scales of minutes to
tens of minutes before the onset of the burst impulsive phase. The 6 cm
burst sources are located close to the neutral line, or near the legs of
a flaring loop. The 20 cm burst sources show complex and extended
structures spatially separated from both the preburst emission and the
gradual decay phase of the burst. The authors interpret the observations
in terms of a two-component flare model (bulk heating as well as
acceleration of particles) and derive the physical parameters of the
burst sources.
@--------------------------------------------------------------------
Title: Erratum - a Study of Flare Buildup from Simultaneous
Observations in Microwave Halpha and Ultraviolet
Wavelengths
Authors: Kundu, M. R.; Gaizauskas, V.; Woodgate, B. E.;
Schmahl, E. J.; Shine, R.; Jones, H. P.
Bibliographic Code: 1985ApJS...58..195K
Abstract
@--------------------------------------------------------------------
Title: Dual frequency observations of solar microwave
bursts using the VLA
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1985ApJ...292..733S
Abstract
Simultaneous observations at 2 and 6 cm wavelengths of a solar active
region and of microwave bursts were carried out with the VLA. The
quiescent 6 cm emission is strongly associated with photospheric
sunspots and is dominated by gyroresonance radiation. The emission at 2
cm, on the other hand, is due to free-free mechanism, and it originates
from the chromosphere-corona transition region. The bursts observed have
multiple peaks. Two-dimensional snapshot maps have been produced at 6
and 2 cm. From the brightness temperature and the degree of circular
polarization, the magnetic field in the microwave burst sources has been
estimated. The generating mechanisms responsible for 6 and 2 cm
radiation are discussed; it is concluded that the 6 cm radiation in the
bursts studied here originates from the bulk heated plasma, whereas the
2 cm radiation is due to the nonthermal particles generated in the
energy-release process.
@--------------------------------------------------------------------
Title: The microwave structure of hot coronal loops
Authors: Holman, G. D.; Kundu, M. R.
Bibliographic Code: 1985ApJ...292..291H
Abstract
The thermal cyclotron emission from model dipole magnetic loops is
computed. It is shown that a simple, isothermal dipole loop can show a
great deal of spatial and polarization structure at microwave
frequencies. This structure is sensitive to the observation frequency
and angle of observation. Two qualitatively distinct microwave loop
structures can be distinguished: (1) 'thin loop,' observed as a string
of independent microwave peaks, corresponding to different harmonics of
the local electron gyrofrequency; and (2) 'thick loop,' the harmonics
are merged, so that a more continuous microwave structure is observed.
It is shown that the presence of an external plasma can result in a
change in the observed mode of polarization along one leg of a loop,
without a change in the sign of the line-of-sight magnetic field. Models
such as these, along with high-resolution microwave and related
observations, can provide an excellent diagnostic of the magnetic and
plasma properties of coronal loops.
@--------------------------------------------------------------------
Title: The sun and nearby stars - Microwave observations at
high resolution
Authors: Kundu, M. R.; Lang, K. R.
Bibliographic Code: 1985Sci...228....9K
Abstract
High-resolution microwave observations are providing new insights into
the nature of active regions and eruptions on the sun and nearby stars.
The strength, evolution, and structure of magnetic fields in coronal
loops can be determined by multiple-wavelength observations with the
Very Large Array. Flare models ccan be tested with Very Large Array
snapshot maps, which have angular resolutions of better than 1 second of
arc in time periods as short as 10 seconds. Magnetic changes that
precede solar eruptions on time scales of tens of minutes involve
primarily emerging coronal loops and the interactions of two or more
loops. Magnetic reconnection at the interface of two closed loops may
accelerate electrons and trigger the release of microwave energy in the
coronal parts of the magnetic loops. Nearby main-sequence stars of late
spectral type emit slowly varying microwave radiation and stellar
microwave bursts that show striking similarities to those of the sun.
@--------------------------------------------------------------------
Title: Book-Review - Unstable Current Systems and Plasma
Instabilities in Astrophysics
Authors: Kundu, M. R.; Holman, G. D.
Bibliographic Code: 1985JBAA...95..139K
Abstract
@--------------------------------------------------------------------
Title: Multiwavelength observations of a preflare solar
active region using the VLA
Authors: Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1985ApJ...291..860K
Abstract
A preflare active region was studied using the Very Large Array at 2, 6,
and 20 cm. At 2 cm the region is composed of two components located in
regions of opposite polarity. Both components are preheated prior to the
impulsive onset of a flare. However, one component develops new
structures during preburst phase, and the burst occurs in this location.
It is believed that the new structures represent emerging flux regions
which interact with an overlying loop to produce a neutral sheet, which
ultimately is responsible for triggering the flare.
@--------------------------------------------------------------------
Title: Observations of Flares at 6 and 20 cm Wavelengths
From Late Type Dwarf Stars UV Ceti and AT Mic
Authors: Kundu, M. R.; Jackson, P. D.; Melozzi, M.
Bibliographic Code: 1985BAAS...17..589K
Abstract
@--------------------------------------------------------------------
Title: Observations of the Cygnus Loop at 40 MHz with the
Clark Lake Teepee Tee
Authors: Jackson, P. D.; Kassim, N. E.; Kundu, M. R.
Bibliographic Code: 1985BAAS...17..545J
Abstract
@--------------------------------------------------------------------
Title: A study of flare buildup from simultaneous
observations in microwave, H-alpha, and UV
wavelengths [ Erratum: 1985ApJS...58..195K ]
Authors: Kundu, M. R.; Gaizauskas, V.; Woodgate, B. E.;
Schmahl, E. J.; Shine, R.; Jones, H. P.
Bibliographic Code: 1985ApJS...57..621K
Abstract
The results of high-resolution observations of the solar preflare
activity of June 25, 1980 are analyzed. The observations were carried
out simultaneously in the UV microwave, and H-alpha wavelengths using
the VLA, the Ottawa River photoheliograph, and the Solar Max
spectrometer and polarimeter instruments. Increases were observed in the
intensitiy and polarization of compact sources at a wavelength of 6-cm
during the preflare hour. The increases were associated with rising and
twisting motions in the magnetic loops near the sight of the subsequent
flare. Consistent with this process, analysis of the transverse and
Doppler motions observed in the H-alpha filament before disruption
showed that the filament was activated internally by the motions of
evolving magnetic flux patterns. Ultraviolet data for C IV brightenings
and upflows at the first appearance of the H-alpha filament indicated
the presence of rising magnetic loops and material rising within the
loops. The complete VLA, microwave and H-alpha data sets are given.
@--------------------------------------------------------------------
Title: Microwave Observations of Solar Active Regions and
Flares Using the Very Large Array
Authors: Kundu, M. R.
Bibliographic Code: 1985spit.conf..503K
Abstract
@--------------------------------------------------------------------
Title: Forty Years of Solar Radio Research
Authors: Kundu, M. R.
Bibliographic Code: 1985spit.conf...23K
Abstract
@--------------------------------------------------------------------
Title: An interpretation of the millisecond time variation
in hard X-ray solar flares
Authors: Krishan, V.; Kundu, M. R.
Bibliographic Code: 1985IAUS..107..299K
Abstract
Recent observations of the fast time variability in the hard X-ray
emission from solar flares are interpreted. The fast spikes are assumed
to be superimposed on the thermal X-ray emission. The rise and fall of a
spike are caused by disruptions in the plasma. The rise time represents
the impulsive heating time and the decay or fall time represents a quick
cooling of the plasma due to the accelerating growth rate of the m = 1
tearing mode. The estimated characteristic time durations of the spike
are found to be in good agreement with the observed ones.
@--------------------------------------------------------------------
Title: The coalescence instability in solar flares
Authors: Tajima, T.; Brunel, F.; Sakai, J.-I.; Vlahos, L.;
Kundu, M. R.
Bibliographic Code: 1985IAUS..107..197T
Abstract
The nonlinear coalescence instability of current carrying solar loops
can explain many of the characteristics of the solar flares such as
their impulsive nature, heating and high energy particle acceleration,
amplitude oscillations of electromagnetic and emission as well as the
characteristics of two-dimensional microwave images obtained during a
flare. The plasma compressibility leads to the explosive phase of loop
coalescence and its overshoot results in amplitude oscillations in
temperatures by adiabatic compression and decompression. It is noted
that the presence of strong electric fields and super-Alfvenic flows
during the course of the instability play an important role in the
production of nonthermal particles. A qualitative explanation on the
physical processes taking place during the nonlinear stages of the
instability is given.
@--------------------------------------------------------------------
Title: Observational evidence for magnetic reconnection in
microwave solar bursts
Authors: Kundu, M. R.
Bibliographic Code: 1985IAUS..107..185K
Abstract
Observations of magnetic reconnection in the solar coronal magnetic
field are presented. The observations were carried out using the NRAO
VLA with a special resolution of 2 arcsec at 6-cm. The period of
observation corresponded to the onset of an impulsive burst observed on
May 14, 1980 at 19:57 UT. A second set of VLA observations of several
interconnecting coronal loops associated with the onset of an impulsive
burst on June 24, 1980, is also presented. The acceleration of electrons
emitting microwaves was observed during magnetic reconnection in both
events. Polarization maps for three selected phases in the evolution of
the burst events are provided.
@--------------------------------------------------------------------
Title: Unstable current systems and plasma instabilities in
astrophysics; Proceedings of the 107th Symposium,
University of Maryland, College Park, August 8-11,
1983
Authors: Kundu, M. R.; Holman, G. D.
Bibliographic Code: 1985IAUS..107.....K
Abstract
Among the topics discussed are: magnetic field reconnection in cosmic
plasmas; energy dissipation mechanisms in the solar corona; and the
acceleration of runaway electrons and Joule heating in solar flares.
Consideration is also given to: the nonlinear evolution of the resistive
tearing mode; anomalous transport in current sheets; equilibrium and
instability in extragalactic jets; and magnetic field reconnection in
differentially rotating accretion disks. Among additional topics
discussed are: the creation of high energy electron tails by lower
hybrid waves and its connection with type-II and type-III bursts; beam
current systems in solar flares; and the spatio-temporal features of
microwave emissions of active regions and flares.
@--------------------------------------------------------------------
Title: Erratum - Microwave Soft and Hard X-Ray Imaging
Observations of Two Solar Flares
Authors: Kundu, M. R.; Machado, M. E.; Erskine, F. T.;
Rovira, M. G.; Schmahl, E. J.
Bibliographic Code: 1984A&A...140..476K
Abstract
@--------------------------------------------------------------------
Title: Center-to-limb variation of a sunspot-associated
microwave source
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1984A&A...139..271A
Abstract
Observations of the simple bipolar active region McMath 16862, obtained
with the Westerbork Synthesis Radio Telescope at 6.16 cm over six
consecutive days, indicate two bright sources associated with the
region's two main spots, as well as some weaker emission that may be
associated with loop structures. Application of a novel analytical
method has allowed the mapping of the vertical as well as the horizontal
component of the sunspot magnetic field at specific locations in the low
corona. While the vertical component decreases away from the source's
center, the horizontal component has both a radial and an azimuthal
part. These results are interpreted in terms of a force-free magnetic
field model, as well as in terms of a dipole whose axis is inclined to
the vertical.
@--------------------------------------------------------------------
Title: Structure and polarization of active region
microwave emission
Authors: Kundu, M. R.; Alissandrakis, C. E.
Bibliographic Code: 1984SoPh...94..249K
Abstract
Active region radio emission observations made at 6.16 cm wavelength
during May 20-27, 1980, are the bases of maps of total intensity and
circular polarization presented for the three regions whose Hale numbers
are 16850, 16863, and 16864. A detailed comparison is made between these
maps and on- and off-band H-alpha pictures and magnetograms. The neutral
lines with which the strongest sources were associated have their two
opposite polarities close to each other, implying a high magnetic field
gradient, and are also associated with arch filament systems. A detailed
analysis is undertaken of observations of the circular polarization
sense inversion in region 16863. The large scale structure of the
magnetic field can be approximated by a dipole with its axis inclined by
11 deg with respect to the photosphere, and with a dipole moment of
about 2 x 10 to the 31 power cgs units.
@--------------------------------------------------------------------
Title: Microbursts at Meter-Decameter Wavelengths
Authors: Kundu, M. R.; Gergely, T. E.; Loiacono, R.
Bibliographic Code: 1984BAAS...16R.892K
Abstract
@--------------------------------------------------------------------
Title: Microwave Emission from Late Type Dwarf Stars UV
Ceti and YZ CMi
Authors: Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1984BAAS...16Q.892K
Abstract
@--------------------------------------------------------------------
Title: Simultaneous Observations of Solar Flares at 6 and
20 cm Wavelengths Using the VLA
Authors: Melozzi, M.; Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1984BAAS...16.1003M
Abstract
@--------------------------------------------------------------------
Title: Microwave and Hard X-ray Imaging of a Solar Limb
Flare
Authors: Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1984BAAS...16.1002S
Abstract
@--------------------------------------------------------------------
Title: Recent advances in solar radio physics
Authors: Kundu, M. R.
Bibliographic Code: 1984InEPS..93..201K
Abstract
High spatial resolution microwave observations of solar active regions,
coronal loops and flares are reviewed. Observations of preflare active
regions are presented; in particular the interpretations of reversal of
polarization at the flare site and the role of newly emerging flux in
triggering the onset of flares are considered. The spatial locations of
microwave burst emitting regions are discussed; loops or arcades of
loops appear to be the sites of flare energy release in microwave
bursts. Direct observational evidence of magnetic reconnection as the
primary cause of acceleration of electrons in microwave bursts is
provided.
@--------------------------------------------------------------------
Title: Coronal extension of flaring region magnetic fields
inferred from high-resolution microwave and type III
burst observations
Authors: Lantos, P.; Pick, M.; Kundu, M. R.
Bibliographic Code: 1984ApJ...283L..71L
Abstract
Observations of three solar radio bursts, obtained with the Very Large
Array of the National Radio Astronomy Observatory at 6 cm wavelength,
have been combined with meter observations from the Mark III Nancay
Radioheliograph. There is a good correlation between solar activity
observed at the two wavelength domains. A small change by about 10 sec
in the centimetric burst location corresponds to a large change, by
about 0.5 solar radius, in the related metric type III burst location.
This indicates discrete injection/acceleration regions and the presence
of very divergent magnetic fields. The bursts come from two distinct
active regions. With two-dimensional spatial resolution, it is shown
that, in this sample, each active region possesses a coronal extension
that is separated from that of the neighboring active region.
@--------------------------------------------------------------------
Title: Three-dimensional structures of two solar active
regions from VLA observations at 2, 6, and 20
centimeter wavelengths
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1984ApJ...283..413S
Abstract
Three-dimensional structures of two active region groups are determined
from observations with the Very Large Array (VLA) at 2, 6, and 20 cm.
One of the groups exhibits a single magnetic loop of length
approximately 10 to the 10th cm. The 2 cm radiation is mostly thermal
bremsstrahlung and originates from the footprints of the loop. The 6 and
20 cm radiation is dominated by low-harmonic gyroresonance radiation and
originates from the upper portion of the legs or the top of the loop.
The loop broadens toward the apex. The top of the loop is not found to
be the hottest point, but two temperature maxima on either side of the
loop apex are observed, which is consistent with the model proposed for
long loops. From 2 and 6 cm observations it can be concluded that the
electron density and temperature cannot be uniform in a plane
perpendicular to the axis of the loop; the density should decrease away
from the axis of the loop.
@--------------------------------------------------------------------
Title: Sharp edges in solar microwave spectra - Neutral
current sheets or cyclotron lines?
Authors: Schmahl, E. J.; Kundu, M. R.; Shevgaonkar, R. K.;
McConnell, D.
Bibliographic Code: 1984SoPh...93..305S
Abstract
Two solar active regions have been mapped using the VLA at three closely
spaced frequencies (4496, 4716, and 4996 MHz) in an attempt to determine
the origin of the steep spectra (index gamma equal to about -5 to -8)
sometimes observed with large single telescopes. One of the regions
observed indeed shows an anomalously large slope (gamma equal to about
-6) compared to the usual (gamma equal to about -2 to -2.5). The other
region shows a similar slope (gamma equal to about -5) but with a larger
range of statistical error. Two possible explanations for such steep
edges in solar spectra are (1) transmission effects of neutral current
sheets, and (2) the appearance of cyclotron lines. The internal evidence
of the microwave maps and simultaneous optical observations favor an
explanation in terms of cyclotron lines.
@--------------------------------------------------------------------
Title: The radio sky from Clark Lake
Authors: Kundu, M. R.
Bibliographic Code: 1984S&T....67..519K
Abstract
The Clark Lake Radio Observatory's telescope is currently the most
sophisticated instrument for low frequency astronomical radio research.
Using this instrument, astronomers have identified an association of
bright X-ray point flares on the sun with the brief, intense radio
bursts, classified as 'Type III', that are generated by the interaction
of electron streams with ambient coronal plasma. Other solar
observations at Clark Lake are of coronal transient shock waves and
plasma cloud distributions. Radio galaxies such as 3C 129 are also
frequent objects of study.
@--------------------------------------------------------------------
Title: The spatial distribution of 6 centimeter
gyroresonance emission from a flaring X-ray loop
Authors: Kahler, S. W.; Webb, D. F.; Davis, J. M.;
Kundu, M. R.
Bibliographic Code: 1984SoPh...92..271K
Abstract
Simultaneous high resolution soft X-ray, and 6-cm images of the decay
phase of an M3 X-ray flare in Hale Region 16413 have been compared. The
X-ray images were obtained with a sounding rocket flown on November 7,
1979 and the 6-cm observations were made with the VLA. A large loop
system approximately 1.3 arc min in length, with an average temperature
of about 8,000,000 K made up the X-ray flare structure. The peak 6-cm
emission seemed to originate from a region below the X-ray loop, and its
predicted flux due to thermal bremsstrahlung was approximately one order
of magnitude less than observed. The expected gyroresonance absorption
is examined through a loop geometry model, and it is found that thermal
gyroresonance emission requiring large azimuthal or radial field
components, or non-thermal gyrosynchrotron emission which involves
continuous electron acceleration, may explain the observations.
@--------------------------------------------------------------------
Title: VLA observations of fine structures in a solar
active region at 6 centimeter wavelength
Authors: McConnell, D.; Kundu, M. R.
Bibliographic Code: 1984ApJ...279..421M
Abstract
A complex solar active region at 6 cm has been observed with the VLA.
Radio images of the region have been constructed and compared with
simultaneous optical data from the region. It is found that all radio
sources are associated with either sunspots or regions of the corona
where strong transverse magnetic fields are likely, that the transverse
field sources are brighter than the sunspot sources, and that some of
the sunspot sources have a polarized ring structure. The observations
are interpreted in terms of thermal gyroresonance emission, with the
radiation from the transverse field sources being at the third harmonic
of the gyrofrequency and predominantly at the second harmonic from the
sunspot sources.
@--------------------------------------------------------------------
Title: The Microwave Structure of Hot Coronal Loops
Authors: Holman, G. D.; Kundu, M. R.; Yang, C.
Bibliographic Code: 1984BAAS...16R.534H
Abstract
@--------------------------------------------------------------------
Title: Simultaneous Dual Wavelength Observations of an
Impulsive Microwave Burst Using the VLA
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1984BAAS...16Q.524S
Abstract
@--------------------------------------------------------------------
Title: Sharp Edges in Solar Microwave Spectra: Neutral
Current Sheets or Cyclotron Lines?
Authors: Schmahl, E. J.; Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1984BAAS...16..534S
Abstract
@--------------------------------------------------------------------
Title: Simultaneous Observation of Hard X-ray and Microwave
Burst Sources in a Limb Flare
Authors: Kundu, M. R.; Takakura, T.
Bibliographic Code: 1984BAAS...16..524K
Abstract
@--------------------------------------------------------------------
Title: Microwave, soft and hard X-ray imaging observations
of two solar flares [ Erratum: 1984A&A...140..476K ]
Authors: Kundu, M. R.; Machado, M. E.; Erskine, F. T.;
Rovira, M. G.; Schmahl, E. J.
Bibliographic Code: 1984A&A...132..241K
Abstract
A set of microwave and hard X-ray observations of two flares observed
simultaneously with the Very Large Array (VLA) and the Solar Maximum
Mission Hard X-ray Imaging Spectrometer (SMM-HXIS) are presented. The
LVA was used at 6 cm to map the slowly varying and burst components in
three neighboring solar active regions (Boulder Nos. 2522, 2530, and
2519) from approximately 14:00 UT until 01:00 UT on June 24-25, 1980.
Six microwave bursts less than 30 sfu were observed, and for the
strongest of these, two-dimensional 'snapshot' (10 s) maps with spatial
resolution of 5 in. were synthesized. HXIS data show clear
interconnections between regions 2522 and 2530. The X-ray observations
present a global picture of flaring activity, while the VLA data show
the complexity of the small magnetic structures associated with the
impulsive phase phenomena. It is seen that energy release did not occur
in a single isolated magnetic structure, but over a large area of
intermingled loop structures.
@--------------------------------------------------------------------
Title: Interpretation of microwave active region structures
using SMM soft X-ray observations
Authors: Strong, K. T.; Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1984ApJ...277..865S
Abstract
The purpose of this paper is to investigate the roles played by the
geometrical effect of gyroresonance absorption and by the
low-temperature (<106K) flux tubes above sunspot regions
with microwave ring structures, by combining WSRT 6 cm observations with
the X-ray observations made with the X-ray Polychromator on the SMM
satellite. Some features associated with Hale regions 16863 and 16864
are analyzed from observations on 1980 May 25 and 26 combined with model
computations of the radio emission. The nature of a cool and compact
coronal feature seen in soft X-rays, which corresponded to some
interesting microwave and magnetic features, is also examined. Finally,
the origin of the X-ray and radio emission associated with neutral lines
of the magnetic field is considered.
@--------------------------------------------------------------------
Title: Radio and visible-light observations of a coronal
arcade transient
Authors: Gergely, T. E.; Kundu, M. R.; Erskine, F. T., III;
Sawyer, C.; Wagner, W. J.; Illing, R.; House, L. L.;
McCabe, M. K.; Stewart, R. T.; Nelson, G. J.
Bibliographic Code: 1984SoPh...90..161G
Abstract
Simultaneous visible-light and radio observations of a coronal transient
that occurred on April 9, 1980 are discussed. Visible-light observations
of the transient and the associated erupting prominence were available
from the Coronagraph/Polarimeter carried aboard SMM, the P78-1
coronagraph, and from the Haleakala Observatory. Radio observations of
the related type III-II-IV bursts were available from the Clark Lake and
Culgoora Observatories. The transient was extremely complex; it is
suggested that an entire coronal arcade rather than just a single loop
participated in the event. Type III burst sources observed at the
beginning of the event were located along a nearby streamer, which was
not disrupted, but was displaced by the outmoving loops. The type II
burst showed large tangential motion, but, unlike such sources usually
do, it had no related herringbone structure. A moving type IV burst
source can be associated with the most dense feature of the white-light
transient.
@--------------------------------------------------------------------
Title: A study of the evolution of energetic electrons in a
solar flare
Authors: Holman, G. D.; Kundu, M. R.; Dennis, B. R.
Bibliographic Code: 1984ApJ...276..761H
Abstract
A study of the impulsive microwave and hard X-ray emissions from the
June 25, 1980 solar flare notes that its light curves are consistent
with the flaring of the regions in unison rather than sequentially, or
in an uncorrelated manner. The maximum 6-cm flux, which occurs 1.4 min
after the maximum in the integrated 28-498 keV X-ray emission, and
coincides with a secondary peak in the X-ray light curve, is explained
by the observation that the X-ray spectrum, and hence that of the
electrons, is harder at the time of the 6-cm flux maximum. The results
show a clear correlation between the X-ray flux greater than 100 keV and
the microwave flux. The steep, low-frequency spectrum at the time of the
6-cm maximum indicates that the emission at this time is nonthermal. The
spectral behavior of the hard X-ray emission is not consistent with the
betatron acceleration mechanism.
@--------------------------------------------------------------------
Title: High spatial resolution microwave observations of
Solar Flares
Authors: Kundu, M. R.
Bibliographic Code: 1984stp..conf..159K
Abstract
@--------------------------------------------------------------------
Title: Millisecond time structures in hard x-ray bursts
from Sun
Authors: Krishan, V.; Kundu, M. R.
Bibliographic Code: 1984stp..conf..147K
Abstract
@--------------------------------------------------------------------
Title: Solar Terrestrial Physics
Authors: Kundu, M. R.; Biswas, B.; Reddy, B. M.;
Ramadurai, S.
Bibliographic Code: 1984stp..conf.....K
Abstract
@--------------------------------------------------------------------
Title: Association Between X-Ray and Meter - Decameter
Bursts (stip Interval Viii)
Authors: Sawant, H. S.; Kane, S. R.; Kundu, M. R.;
Gergely, T. E.
Bibliographic Code: 1984sii..conf..113S
Abstract
@--------------------------------------------------------------------
Title: Recent advances in solar radio physics.
Authors: Kundu, M. R.
Bibliographic Code: 1984PIASE..93..201K
Abstract
The author reviews high spatial resolution microwave observations of
solar active regions, coronal loops and flares. Observations of preflare
active regions are presented; in particular the author discusses the
interpretations of reversal of polarization at the flare site and the
role of newly emerging flux in triggering the onset of flares. He
discusses the spatial locations of microwave burst emitting regions;
loops or arcades of loops appear to be the sites of flare energy release
in microwave bursts.
@--------------------------------------------------------------------
Title: Coronal transients and their interplanetary effects.
Authors: Hundhausen, A. J.; Burlaga, L. F.; Feldman, W. C.;
Gosling, J. T.; Hildner, E.; House, L. L.;
Howard, R. A.; Krieger, A. S.; Kundu, M. R.;
Low, B. C.; Sheeley, N. R., Jr.; Steinolfson, R. S.;
Stewart, R. T.; Stone, R. G.; Wu, S. T.
Bibliographic Code: 1984NASRP1120....6H
Abstract
Contents: 1. Introduction. 2. Background material: Ancient history -
solar flares and geomagnetic storms. Modern history - interplanetary
shock waves. Coronal transients or mass ejections. 3. The present:
Theoretical models. New observations of coronal mass ejections. 4. The
future: Solar origins. Interplanetary effects.
@--------------------------------------------------------------------
Title: Relative positions of microwave and hard X-ray burst
sources
Authors: Kundu, M. R.
Bibliographic Code: 1984AdSpR...4Q.157K
Abstract
Simultaneous microwave and hard X-ray imaging observations of 12 bursts
show that it is difficult to discern a general pattern between microwave
and hard X-ray burst locations. In general, the microwave source is
displaced from the hard X-ray source. The commonly believed behavior of
the microwave source being located near the top and hard X-ray source
near the footpoints of a loop appears to be true in some cases but not
all. If the burst source is simple, both may be located near loop tops.
Sometimes when the hard X-ray source has two components, one weak and
one strong, the microwave source is not located over a neutral line
(loop top) but close to a sunspot where the magnetic field is strongest.
It appears that more than one loop or arcade may sometimes be involved
in the microwave and hard X-ray emission. This is particularly true when
several interacting loops trigger the onset of a flare.
@--------------------------------------------------------------------
Title: A multiple type-II burst associated with a coronal
transient and its MHD simulation
Authors: Gergely, T. E.; Kundu, M. R.; Wu, S. T.; Dryer, M.;
Smith, Z.; Stewart, R. T.
Bibliographic Code: 1984AdSpR...4..283G
Abstract
A large coronal transient took place on May 8, 1981. The transient was
related to an M7.7/2B flare and was associated with at least two coronal
type-II bursts. The velocities of the type-II bursts were in the range
1100-1800 km/s, in excess of the transient velocity of 1000 km/s. Two
dimensional positions of the type-II radio sources are available from
both the Clark Lake and the Culgoora Radio Observatories. Two
dimensional MHD simulations of the event are carried out, taking into
account the observed velocity, position, and size of the type-II bursts.
The multiple shocks observed during the event and their interaction are
simulated, and results of the simulation are discussed.
@--------------------------------------------------------------------
Title: Observations of solar radio bursts from meter to
kilometer wavelengths
Authors: Kundu, M. R.; Stone, R. G.
Bibliographic Code: 1984AdSpR...4..261K
Abstract
New results obtained with the Clark Lake multifrequency radioheliograph
at meter-decameter wavelengths and from satellite multifrequency
directive observations at hectometer and kilometer wavelengths are
reviewed. Evidence is presented that type III electrons propagate in
dense coronal streamers and that frequently observed microbursts
(presumably type III) at meter-decameter wavelengths are due to plasma
radiation. Observations of hectometer and kilometer type III radio
storms which reveal information about active region structures, the
interplanetary magnetic field configuration, and solar wind acceleration
are discussed. Kilometer type II bursts and interactions between type
III electrons and interplanetary shocks are examined, and some new
results on shock-associated events are presented.
@--------------------------------------------------------------------
Title: Simultaneous dual wavelength observations of an
impulsive microwave burst using the V.L.A
Authors: Shevgaonkar, R. K.; Kundu, M. R.
Bibliographic Code: 1984AdSpR...4..247S
Abstract
Simultaneous observations of a microwave burst at 2 and 6 cm wavelengths
were carried out with the Very Large Array (VLA). The 6 cm burst source
is located close to a magnetic neutral line, presumably near the top of
a flaring loop, while the 2 cm emission originates from the footpoints
of the loop. It is concluded that the 6 cm emission is dominated by
gyrosynchrotron radiation of the thermal electrons in the bulk heated
plasma at a temperature of approximately 4 x 10 to the 7th K, while the
2 cm emission is due to nonthermal particles released and accelerated
during the flare process. From the observed low degree of polarization
and the lack of the 2 cm source cospatially with the 6 cm source a
magnetic field of 200-350 G and delta approximately equal to or greater
than 4 are estimated in the flare energy release site. A DC electric
field flare model is invoked to explain the long delay between the peaks
at the two wavelengths. From the delay, the strength of the electric
field is estimated to be 0.2-4 micro statvolt/cm in the flaring region.
@--------------------------------------------------------------------
Title: VLA observations of 'compact' sources in CTB 80
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1983JApA....4..253V
Abstract
High resolution (3 arcsec-4 arcsec) maps of three compact sources in CTB
80, observed with the Very Large Array at 6 and 20 cm wavelengths are
presented. The central core consists of a limb-brightened shell (of
diameter 30 arcsec) superimposed on a diffuse emission of size 75 arcsec
x 45 arcsec. The compact sources 1949+324 and 1952+332 located near the
tips of the southwest and northeast ridges are rather remarkable and
possibilities for these to be fragments ejected by the SN are examined.
1949+324 is fully resolved by the 4 arcsec beam and shows structure with
multiple components oriented perpendicular to the ridge. 1950+326 is a
background radio source.
@--------------------------------------------------------------------
Title: Optical, microwave and UV imagery of a solar flare.
Authors: Gaizauskas, V.; Kundu, M. R.; Schmahl, E. J.;
Shine, R. A.; Woodgate, B. E.
Bibliographic Code: 1983JRASC..77..261G
Abstract
@--------------------------------------------------------------------
Title: The Thermal Phase of Flares: A New Diagnostic Using
Microwaves &GOES X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Erskine, F. E.
Bibliographic Code: 1983BAAS...15..972S
Abstract
@--------------------------------------------------------------------
Title: Three Dimensional Structures of Solar Active Regions
and Flare Buildup from VLA Observations
Authors: Kundu, M. R.; Shevgaonkar, R. K.
Bibliographic Code: 1983BAAS...15..972K
Abstract
@--------------------------------------------------------------------
Title: Spatial characteristics of microwave bursts
Authors: Kundu, M. R.
Bibliographic Code: 1983SoPh...86..205K
Abstract
The spatial characteristics of microwave bursts are examined in relation
to impulsive and post-burst phases using data collected by the Very
Large Array and the Westerbork Synthesis Radio Telescope. The existence
of a gradual and a spiky component in the impulsive phase is examined
using high time and spatial resolution observations. It is proposed that
homologous flares exist at 6 cm, based on the similarity of their
spatial structure and their temporal evolution. Preflare changes in
microwave active regions are studied in terms of newly emerging flux at
the flare site. High spatial resolution observations of the structure of
microwave flaring loops are interpreted in terms of arcades of loops at
the sites of primary energy release. The relative timing of the peaks of
impulsive hard X-ray and microwave bursts is analyzed. The role of the
emergence of new flux and of the current sheet formed between closed
loops in producing impulsive energy release at centimeter wavelengths is
examined.
@--------------------------------------------------------------------
Title: X-ray and microwave observations of active regions
Authors: Webb, D. F.; Davis, J. M.; Kundu, M. R.;
Velusamy, T.
Bibliographic Code: 1983SoPh...85..267W
Abstract
Coordinated high-resolution (1-3 arcsec) observations of two active
solar regions (H 421 and H 419) on November 16, 1979, are reported:
soft-X-ray filtergrams from a sounding rocket flight, VLA
total-intensity and circular-polarization microwave (6-cm) radio maps,
KPNO full-disk photospheric magnetograms, and BBSO H-alpha data. The
images were converted to 4.8-arcsec/mm-scale transparencies and
coaligned on the basis of sunspot positions for comparison. The two
active regions are characterized in detail, and intensity, size, and
polarization data for the brightest microwave components (BMC) are
listed. It is found that 19 of the 32 BMC are farther than 5 arcsec from
any sunspot, and that X-ray-emitting structures only rarely correspond
to sunspots, or BMC. About one third of the BMC are located at the feet
or legs of coronal loops smaller than about 50,000 km. The limitations
implied by these obervations for proposed thermal-bremsstrahlung,
thermal-gyro-resonance, and nonthermal microwave-emission mechanisms are
discussed.
@--------------------------------------------------------------------
Title: Network to cell contrast at microwaves
Authors: Chiuderi Drago, F.; Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1983SoPh...85..237C
Abstract
The expected contrast between bright and dark elements in the solar
atmosphere are calculated for the 3 mm-10 cm radio wavelength range
using previous models devised from EUV line intensity data. The
brightness was computed in relation to the cell center, and average
network differential emission measure, assuming a temperature range of
89,000-1,000,000 K. The radio temperature attributable to free-free
emission is integrated for the presence and absence of a magnetic field,
which when in evidence varies with height above the solar surface.
Consideration is given to the behavior of the network projected by four
different analytical models in relation to the frequencies of
temperature changes and average contrasts. It is found that the
inhomogeneities in the quiet sun at mm and cm radio wavelengths are
consistent with the cell and network structure observed in the Ca II
lines in the solar chromosphere.
@--------------------------------------------------------------------
Title: Direct evidence of type III electron streams
propagating in coronal streamers
Authors: Kundu, M. R.; Gergely, T. E.; Turner, P. J.;
Howard, R. A.
Bibliographic Code: 1983ApJ...269L..67K
Abstract
Using two-dimensional solar images at 73.8 MHz, obtained with the Clark
Lake Multifrequency Radioheliograph, the authors present direct evidence
that type III electron streams propagate in dense coronal streamers.
This evidence is substantiated by the excellent coincidence that is
found in position angle between the densest parts of streamers observed
with the Solwind coronagraph on the P78-1 satellite and the maximum
brightness of type III burst sources.
@--------------------------------------------------------------------
Title: VLA observations of a solar active region and
coronal loops
Authors: McConnell, D.; Kundu, M. R.
Bibliographic Code: 1983ApJ...269..698M
Abstract
In May 1981, observations of a solar active region at 6 cm and 20 cm
were conducted with the aid of a Very Large Array (VLA). It was found
that the 6 cm emission was associated with sunspots and transverse
magnetic fields between spots. The 20 cm emission came from elongated
sources connecting regions of opposite magnetic polarity. The sources of
the emission at 20 cm could be identified as coronal loops. A model for
hydrostatic loops proposed by Rosner et al. (1978) was employed to
determine a likely mechanism for the emission at 20 cm. It was found
that a two-component model of bremsstrahlung emission from the feet and
gyroresonance emission from the top of the loops can satisfactorily
explain the observations.
@--------------------------------------------------------------------
Title: A coronal transient associated with a high-speed
type II burst
Authors: Gergely, T. E.; Kundu, M. R.; Hildner, E.
Bibliographic Code: 1983ApJ...268..403G
Abstract
Several characteristics of a white light transient observed by the ATM
Coronagraph experiment aboard Skylab are discussed. The transient was
associated with a very high speed type II radio burst. The observed
plane of the sky speed of the burst was 4900 km/s, 6-7 times higher than
the speed of the transient itself. Based on the relative speeds of the
transient and the radio burst, it is argued that the type II disturbance
must have propagated in a still undisturbed corona, at an approximately
35-deg angle to the preexisting streamer and along an essentially open
field configuration. The electron density gradients derived from the
radio and the white light observations are compared, and it is shown
that they are in agreement within the limits of the observations. The
assumption that the type II was a weak MHD shock leads to large values
for the coronal magnetic field. The possibility that the type II
radition originated in a strong shock, with a magnetic Mach number
greater than 2, is considered.
@--------------------------------------------------------------------
Title: Ground based solar radio observations during solar
maximum mission
Authors: Kundu, M. R.
Bibliographic Code: 1983STIN...8320887K
Abstract
The Very Large Array (VLA) and the Westerbork Synthesis Radio Telescope
(WSRT) were used for making aperture synthesis maps of solar active and
flaring regions. Observations of the Flare buildup in the form of
increased intensity and polarization were made. Ring structure
associated with sunspots were interpreted as due to the existence of
cool material above the spot. Model computations were performed to
explain the total intensity and polarization structures of a continuous
set of active region maps.
@--------------------------------------------------------------------
Title: First results from the Clark Lake Multifrequency
Radioheliograph
Authors: Kundu, M. R.; Erickson, W. C.; Gergely, T. E.;
Mahoney, M. J.; Turner, P. J.
Bibliographic Code: 1983SoPh...83..385K
Abstract
The characteristics of the Clark Lake Multifrequency Radioheliograph,
which is presently being used for solar research in the frequency range
20-125 MHz, are examined and several solar maps obtained with this
instrument are presented. Two-dimensional images of the sun's corona at
several frequencies within this range are examined, which were obtained
with time resolution as good as 1.28 s. It is found that the shape of
the sun's outer corona as observed at meter-decameter wavelengths
appears to change in time periods as short as a few seconds.
@--------------------------------------------------------------------
Title: Decameter Wavelength Observations of the Quiet Sun
Authors: Gergely, T. E.; Gross, B. D.; Kundu, M. R.
Bibliographic Code: 1983BAAS...15Q.716G
Abstract
@--------------------------------------------------------------------
Title: Microwave, Soft and Hard X-ray Imaging Observations
of Two Solar Flares
Authors: Kundu, M. R.; Machado, M.; Erskine, F. T.;
Rovira, M. G.; Schmahl, E. J.
Bibliographic Code: 1983BAAS...15..714K
Abstract
@--------------------------------------------------------------------
Title: Thermal and nonthermal phenomena in solar flare
loops at 20 CM wavelength and in X-rays
Authors: Schmahl, E. J.; Kundu, M. R.; Landecker, P. B.;
McKenzie, D. L.
Bibliographic Code: 1983SoPh...83....3S
Abstract
X-ray images from the P78-1 satellite are presented for a long-lasting
burst at 20 cm wavelength mapped with the Very Large Array on May 19,
1979. The decimeter wave observations were originally interpreted in
terms of two models, one invoking thermal electrons radiating at low
harmonics of the gyrofrequency, and the other invoking mildly
relativistic electrons emitting gyrosynchrotron radiation. If the 20 cm
source is thermal, it should also be visible in soft X-rays, while if it
is nonthermal, the soft X-ray emission should be weak or spatially or
temporally distinct from the 20 cm burst. It is found that only one of
the three 20 cm sources was approximately co-spatial with the soft X-ray
source, and that it was only partially thermal. The 20 cm burst is
therefore primarily decimeter type IV emission from mildly relativistic
electrons of the post-flare phase. The over 2 hr lifetime and smooth
temporal variation of the burst belie its nonthermal nature and suggest
continuous acceleration as well as long-term storage of energetic
electrons.
@--------------------------------------------------------------------
Title: Observations of H-alpha and microwave brightening
caused by a distant solar flare
Authors: Kundu, M. R.; Rust, D. M.; Bobrowsky, M.
Bibliographic Code: 1983ApJ...265.1084K
Abstract
Three subflares were observed at 6 cm lambda and at Halpha (6563
Å) with the VLA and the Solar Observing Optical Network high
resolution telescopes. Synthesized maps with integration times of 10 and
30 s show that most of the 6 cm burst emission originated in
≡10arcsec - 15arcsec features coincident with or adjacent to
Halpha flare kernels. During the onset of one of the subflares 6 cm
emission was discovered in a loop stretching >105 km from
the primary flare site; this emission was associated with faint Halpha
flarelike brightness at the remote footpoint of the loop. Assuming that
the energy for the distant brightening originated at the primary flare
site, it is found that ≡4 × 1024 ergs
s-1 propagated along the connecting magnetic loop at a
velocity of >= 6000 km s-1. Various possible mechanisms for
the distant activation are discussed.
@--------------------------------------------------------------------
Title: Magnetic development of flaring regions at
centimeter wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1983ASSL..102..335K
Abstract
A hard X-ray associated impulsive 6 cm burst observed by Kundu et al.
(1981) on June 25, 1980, is considered along with several preflare 6 cm
maps related to this event. The maps show that the region is very
complex and consists of numerous components. Many of these components
are bipolar. The components have brightness temperatures in the range
from 6,000,000 to 9,000,000 K during the hour before the flare. Some of
the observed phenomena might imply the emergence of a flux of reverse
polarity at coronal levels. It is believed that the reverse polarity may
be caused by the expansion of a preexisting flux tube in which twisting
increases its coronal magnetic field.
@--------------------------------------------------------------------
Title: Solar microwave bursts - A review
Authors: Kundu, M. R.; Vlahos, L.
Bibliographic Code: 1982SSRv...32..405K
Abstract
Observational and theoretical results on the physics of microwave bursts
that occur in the solar atmosphere are reviewed. Special attention is
given to the advances made in burst physics over the last few years with
the great improvement in spatial and time resolution, especially with
instruments like the NRAO three-element interferometer, the Westerbork
Synthesis Radio Telescope, and more recently the Very Large Array.
Observations made on the preflare build-up of an active region at
centimeter wavelengths are reviewed. Three distinct phases in the
evolution of cm bursts, namely the impulsive phase, the post-burst
phase, and the gradual rise and fall, are discussed. Attention is also
given to the flux density spectra of centimeter bursts. Descriptions are
given of observations of fine structures with temporal resolution of
10-100 ms in the intensity profiles of cm-wavelength bursts. High
spatial resolution observations are analyzed, with special reference to
the one- and two-dimensional maps of cm burst sources.
@--------------------------------------------------------------------
Title: Advances in solar radio astronomy
Authors: Kundu, M. R.
Bibliographic Code: 1982RPPh...45.1435K
Abstract
The status of the observations and interpretations of the sun's radio
emission covering the entire radio spectrum from millimeter wavelengths
to hectometer and kilometer wavelengths is reviewed. Emphasis is given
to the progress made in solar radio physics as a result of recent
advances in plasma and radiation theory. It is noted that the capability
now exists of observing the sun with a spatial resolution of
approximately a second of arc and a temporal resolution of about a
millisecond at centimeter wavelengths and of obtaining fast
multifrequency two-dimensional pictures of the sun at meter and
decameter wavelengths. A summary is given of the properties of
nonflaring active regions at millimeter, centimeter, and meter-decameter
wavelengths. The properties of centimeter wave bursts are discussed in
connection with the high spatial resolution observations. The
observations of the preflare build-up of an active region are reviewed.
High spatial resolution observations (a few seconds of arc to
approximately 1 arcsec) are discussed, with particular attention given
to the one- and two-dimensional maps of centimeter-wavelength burst
sources.
@--------------------------------------------------------------------
Title: Active region magnetic fields inferred from
simultaneous VLA microwave maps, X-ray
spectroheliograms, and magnetograms
Authors: Schmahl, E. J.; Kundu, M. R.; Strong, K. T.;
Bentley, R. D.; Smith, J. B., Jr.; Krall, K. R.
Bibliographic Code: 1982SoPh...80..233S
Abstract
The VLA maps at 6-cm wavelength discussed here are generated from
observations of a solar active region (NOAA 2363) on March 29 and 30,
1980. The X-ray spectroheliograms were acquired for this region in the
lines of O VIII, Ne IX, Mg XI, Si XIII, S XV, and Fe XXV. It is found
that the peaks of X-ray and 6-cm emission do not coincide but that the
sources in the two wavelength domains tend to overlap. These facts are
seen as evidence for the existence of opacity mechanisms other than
thermal bremsstrahlung. To quantify this assertion, differential
emission measures are computed to derive densities and temperatures.
Using these and calculated force-free magnetic fields from Kitt Peak
magnetograms, an assessment is made of the mechanism of gyroresonance
absorption at low harmonics of the electron gyrofrequency as the source
of opacity responsible for the microwave features. It is concluded that
large-scale currents must be present in the active region loops to
account for the bright 6-cm sources far from sunspots.
@--------------------------------------------------------------------
Title: VLA Observations of Dramatic Changes in Fine
Structure of Solar Active Regions
Authors: Schmahl, E. J.; McConnell, D. M.; Kundu, M. R.
Bibliographic Code: 1982BAAS...14..924S
Abstract
@--------------------------------------------------------------------
Title: Correspondence Between 6 cm and Optical Images of a
Solar Active Region
Authors: McConnell, D.; Schmahl, E. J.; Kundu, M. R.
Bibliographic Code: 1982BAAS...14..921M
Abstract
@--------------------------------------------------------------------
Title: Positional characteristics of meter-decameter
wavelength bursts associated with hard X-ray bursts
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.
Bibliographic Code: 1982SoPh...79..107K
Abstract
Isolated and grouped type III bursts have been observed in temporal
association with impulsive hard X-ray bursts in the 26-154 keV range,
down to frequencies as low as 30 MHz and out to a distance of 3.1 solar
radii from the disk center. The bursts occurred in regions whose
electron density may have been as much as 20 times higher than that of
the Newkirk-Saito model. The present observations indicate that electron
acceleration/injection occurs over a region covering a wide range of
magnetic field lines. It is noted that, of the two gradual hard X-ray
bursts observed in association with type IV bursts, one was accompanied
by a type II event, while the other was not, although both exhibited the
same characteristics. It is suggested that the gradual burst associated
with a type IV only involved electrons which are trapped in the plasmoid
which produces the meter-decameter emission, while another fraction of
the population is trapped in the low-lying loops which produce the hard
X-ray and centimeter radiation.
@--------------------------------------------------------------------
Title: Probing the radio sun
Authors: Kundu, M. R.
Bibliographic Code: 1982S&T....64....6K
Abstract
Radio studies of solar flares by the Very Large Array (VLA) of the
National Radio Astronomy Observatory are discussed along with the
results of cm and X-ray observations of flares. The synthesis of maps of
regions of the sun just prior to flares and the validation of solar
flare models using VLA are treated. Theories of the source of a flare's
energy, and of the processes that produce one, are summarized. One
unusual flare is cited as support for the flare model in which a current
sheet develops at the interface between two closed loops.
@--------------------------------------------------------------------
Title: VLA observations of the evolution of a solar burst
source structure at 6 centimeter wavelength
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1982ApJ...258..388V
Abstract
Evolutionary changes in the total intensity and polarization structure
of a 6 cm radio burst source have been observed with the VLA, over time
scales ranging from 10 s to several minutes. This burst was associated
with a 2B/M1 flare observed on 1980 May 14. The 6 cm burst consisted of
a gradual phase of 30 minutes duration and a strong impulsive phase of
duration less than two minutes. Synthesized maps of total intensity and
polarization were obtained with spatial resolution of 2 x 3 arcsec and
with temporal resolutions of five minutes during the gradual phase and
10 s during the impulsive phase. The sequence of polarization maps
suggests a complex magnetic field structure undergoing rapid changes.
Most importantly, they show the development of two bipolar regions or
quadrupole structure just prior to the impulsive energy release.
@--------------------------------------------------------------------
Title: Electron pitch angle scattering and the impulsive
phase microwave and hard X-ray emission from solar
flares
Authors: Holman, G. D.; Kundu, M. R.; Papadopoulos, K.
Bibliographic Code: 1982ApJ...257..354H
Abstract
Observations and theoretical considerations have led to a model for
impulsive phase flare emission involving the heating and acceleration of
thermal electrons in the coronal part of a magnetic loop. The bulk of
the heated gas is confined between conduction fronts, but particles with
velocities a few times greater than the thermal velocity can escape into
the lower part of the loop. It is shown that, when the electron
gyrofrequency exceeds the plasma frequency, the escaping electrons are
unstable to the generation of electrostatic plasma waves which scatter
the particles in pitch angle to a nearly isotropic distribution. It is
also shown that this scattering can (1) enhance the microwave emission
from the upper part of the loop, and (2) due to the Landau damping of
both low and high phase velocity waves, can lead to one or two breaks in
the impulsive-phase hard X-ray spectrum.
@--------------------------------------------------------------------
Title: Positions of type II fundamental and harmonic
sources in the 30-100 MHZ range
Authors: Sawant, H. S.; Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1982SoPh...77..249S
Abstract
An excellent example of a type III-V burst followed by a type II burst
with fundamental and harmonic bands was observed on June 18, 1979 at the
Clark Lake Radio Observatory. The observations are described in detail
and their implications are discussed with regard to the problem of
directionality with respect to the magnetic field lines of the
collisionless MHD shock wave generated at the start of the flash phase.
It is found that the positions of type III and type II (F) bursts at a
number of frequencies are essentially the same, which implies that the
shock responsible for the type II radiation follows the path of the type
III exciter, that is, the shock propagates along the open field lines.
@--------------------------------------------------------------------
Title: Radio imaging of solar flares using the very large
array - New insights into flare process
Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T.;
Vlahos, L.
Bibliographic Code: 1982A&A...108..188K
Abstract
An interpretation of VLA observations of microwave bursts is presented
in an attempt to distinguish between certain models of flares. The VLA
observations provide information about the pre-flare magnetic field
topology and the existence of mildly relativistic electrons accelerated
during flares. Examples are shown of changes in magnetic field topology
in the hour before flares. In one case, new bipolar loops appear to
emerge, which is an essential component of the model developed by
Heyvaerts et al. (1977). In another case, a quadrupole structure,
suggestive of two juxtaposed bipolar loops, appears to trigger the
flare. Because of the observed diversity of magnetic field topologies in
microwave bursts, it is believed that the magnetic energy must be
dissipated in more than one way. The VLA observations are clearly
providing means for sorting out the diverse flare models.
@--------------------------------------------------------------------
Title: Time variability and structure of quiet sun sources
at 6 CM wavelength
Authors: Erskine, F. T.; Kundu, M. R.
Bibliographic Code: 1982SoPh...76..221E
Abstract
Results are presented of a detailed study of quiet sun emitting regions
at 6 cm and their correspondence with regions observed at optical
wavelengths. The Westerbork Synthesis Radio Telescope was used to obtain
a 12-hr synthesis map of a quiet sun region with a resolution of 6
arcsec. Comparison of this map with a Ca(+) K filtergram indicates the
features on the 6-cm map to correspond to Ca(+) K chromospheric networks
and cells. In addition, about 72% of the magnetic field enhancements
observed on photospheric magnetograms coincides with 6-cm emissive
regions. Intercomparison of the 12-hr synthesis map, a 4-hr synthesis
map and 6-cm fan beam scans along with the Ca(+) K and magnetogram
results reveals all of the time-varying 6-cm elements to be located on
Ca(+) K networks, and about 40% of them to be coincident with
magnetogram enhancements. Lifetimes of the time-varying sources vary
from a few minutes to several tens of minutes, and intensity varies by
factors of 2 to 7.
@--------------------------------------------------------------------
Title: Observations of ring structure in a sunspot
associated source at 6 centimeter wavelength
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1982ApJ...253L..49A
Abstract
The detection of a new kind of sunspot-associated source in which the
emission comes predominantly from a ring structure with size between
that of the umbra and the penumbra is reported. The absence of emission
from the center of the spot is interpreted in terms of the orientation
of the magnetic field and the presence of low temperature material above
the umbra.
@--------------------------------------------------------------------
Title: Magnetic structure of a flaring region producing
impulsive microwave and hard X-ray bursts
Authors: Kundu, M. R.; Schmahl, E. J.; Velusamy, T.
Bibliographic Code: 1982ApJ...253..963K
Abstract
Using VLA observations of the 1B/M1 flare of June 25, 1980, 6-cm
'snapshot' maps are synthesized. The spatial and temporal resolutions
during the 9 minutes of the impulsive phase were, respectively, 1 arcsec
x 2 arcsec and 10 s. Some displacement is noted between the locations of
the burst source and the preflare loop structures seen in the preflare
map. The burst peak occurred on the neutral line of the preflare
polarization map, between the two oppositely polarized microwave 'loop'
structures approximately 40 arcsec long. Concurrent hard X-ray
observations were made of the burst, although these had no spatial
resolution. The 6-cm maps show the locations of a number of the X-ray
burst spikes. The 6-cm burst was fully resolved into at least eight
components, many of which were bipolar.
@--------------------------------------------------------------------
Title: Simultaneous mapping of microwave burst sources with
the VLA at 2, 6 and 20 cm wavelengths.
Authors: Kundu, M. R.; Velusamy, T.; McConnell, D.
Bibliographic Code: 1982BAAS...14..572K
Abstract
@--------------------------------------------------------------------
Title: Centimeter Wavelength Observations of Active Regions
and Flares with a Few Arc-Second Resolution
Authors: Kundu, M. R.
Bibliographic Code: 1982coas.conf..119K
Abstract
@--------------------------------------------------------------------
Title: Physics of the impulsive phase of solar flares
Authors: Kundu, M. R.
Bibliographic Code: 1982AdSpR...2..159K
Abstract
A review is presented of the physics of the impulsive phase of solar
flares in relation to high resolution microwave, hard X-ray, and
ultraviolet observations based on research done on the Impulsive Phase
of Flares during the Solar Maximum Year. High spatial resolution
observations are presented of the structure of microwave flaring loops
as well as their interpretations in terms of arcades of loops as the
sites of primary energy release. High temporal and spatial resolution
measurements in hard X-rays and observations of the relative locations
of microwave and hard X-ray emitting regions are presented and their
significance with respect to the energy release site and the electron
acceleration is examined. Also considered is the relative timing of the
peaks of impulsive hard X-ray and microwave burst, as well as the
significance of ultraviolet measurements in obtaining the density of
flaring regions. In addition, decimeter and meter wave manifestations of
preflash phase and millisecond pulsations at centimeter and decimeter
wavelengths and the relevant physical processes involved are examined.
@--------------------------------------------------------------------
Title: VLA observations of positions 42 6 centimeter burst
peaks associated with hard X-ray burst spikes
Authors: Kundu, M. R.; Bobrowsky, M.; Velusamy, T.
Bibliographic Code: 1981ApJ...251..342K
Abstract
Using the Very Large Array with a spatial resolution of 3 arcsec,
two-dimensional, 10-second synthesis maps are produced of four 6-cm
lambda bursts associated with multiply spiked hard X-ray bursts (20-300
keV). The positional, structural, and polarization characteristics are
investigated. It is noted that three of the four burst sources are
rather compact (less than approximately 10 arcsec). It is found that the
positions of the individual peaks or spikes within a single burst are
the same within plus or minus 2 arcsec. Interpreting these different
peaks as separate electron acceleration events, the results suggest
repeated acceleration of electrons within the same magnetic trap. The
trap situation is found to be consistent with the bipolar nature of the
burst sources except in one case.
@--------------------------------------------------------------------
Title: New meter-wavelength observations of S 147
Authors: Angerhofer, P. E.; Kundu, M. R.
Bibliographic Code: 1981AJ.....86.1003A
Abstract
High-resolution 430-MHz (69.8 cm) continuum observations of the galactic
supernova remnant S 147 are presented. The presence of embedded numerous
small-diameter radio sources producing a well defined radio shell, and a
pronounced break in the flux density spectrum are suggested. Four 4C
sources, several B2 sources and three anonymous sources are included,
and the mean spectral index of these sources is found to be
significantly less than that of typical extragalactic sources. Due to
the distribution of the angular diameters, it is also suggested that the
sources belong to the galactic sources, although the numbers do not
represent an excess over that expected from background source counts. It
is concluded that S 147 is in a relatively late stage of remnant
evolution, and the sources may be a result of ionization of neutral
material by the advancing shock.
@--------------------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun - I.A.U.
SYMP.86
Authors: Kundu, M. R.; Gergeley, T. E.; Kruger, A.
Bibliographic Code: 1981SSRv...28..223K
Abstract
@--------------------------------------------------------------------
Title: Observations of solar filaments at 8, 15, 22 and 43
GHz
Authors: Schmahl, E. J.; Bobrowsky, M.; Kundu, M. R.
Bibliographic Code: 1981SoPh...71..311S
Abstract
Radio depressions frequently appear broader than their associated
H-alpha filaments and often persist after a filament disappears. The
reported study is concerned with the relative contributions of filament
and the filament channel to the depth of radio depressions. Although the
contribution cannot readily be determined in an individual case, the
apportionment can be assessed statistically by extensive multi-frequency
observations of many filaments and channels using the same telescope
over a period of days. In principle it is possible to determine the
evolution, geometry, and physical properties of filaments and filament
channels with a widely based set of radio observations. It is found that
all but a few percent of the microwave depressions lie on magnetic
neutral lines or their natural extensions. The only possible exceptions
are coronal holes on the disk, which are small or non-existent during
the period of the conducted observations. The diversity of microwave
filaments is striking. Even quiescent filaments show considerable
variation.
@--------------------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun
Authors: Kundu, M. R.; Gergely, T. E.; Layzer, D.
Bibliographic Code: 1981Natur.291..518K
Abstract
@--------------------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun
Authors: Layzer, D.; Kundu, M. R.; Gergely, T. E.
Bibliographic Code: 1981Natur.291..517L
Abstract
@--------------------------------------------------------------------
Title: Decameter studies of the 5 September 1973 flare
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1981SoPh...71...65G
Abstract
The spectra and positions of the meter-decameter wavelength radio
sources associated with the flare of September 5, 1973 are discussed.
The evolution of the size of the type II burst source is discussed and
it is shown that it fluctuates by a factor of 10, or larger.
Consequently, the potential and kinetic energies associated with the
shock are uncertain by the same factor. By a comparison of the positions
of the type II and type III sources, it is concluded that while the
shock wave associated with the type II was guided along high loops, the
type III electrons were injected along open field lines which diverged
within a short height in the corona. The characteristics of a
particularly interesting type III burst with a low-frequency cut-off are
discussed. It is argued that nearby loops were not disrupted by the
shock and that the energetic electrons produced during the event must
have been injected at several sites and guided along open field lines at
large distances from the flare to produce type III bursts.
@--------------------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun - IAU SYMP.86
Authors: Kundu, M. R.; Gergely, T. E.
Bibliographic Code: 1981Sci...212...90K
Abstract
@--------------------------------------------------------------------
Title: VLA search for radio emission from stars with
solar-type structures
Authors: Bowers, P. F.; Kundu, M. R.
Bibliographic Code: 1981AJ.....86..569B
Abstract
Results are presented of a high-sensitivity search for 6-cm radio
emission from stars with evidence of active chromospheric or coronal
regions. The data indicate that many of these stars have radio
luminosities much less than those that have been found for known radio
stars.
@--------------------------------------------------------------------
Title: Two-Dimensional Radioheliographic Pictures of the
Sun's Outer Corona at 25.6-110.6 MHz
Authors: Kundu, M. R.; Erickson, W. C.; Turner, P. J.
Bibliographic Code: 1981BAAS...13Q.891K
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of Solar Flares and Tests of Flare
Models
Authors: Kundu, M. R.
Bibliographic Code: 1981BAAS...13..909K
Abstract
@--------------------------------------------------------------------
Title: Active Region Magnetic Fields
Authors: Smith, J. B., Jr.; Strong, K. T.; Schmahl, E. J.;
Kundu, M. R.; Krall, K. R.; Bentley, R. D.
Bibliographic Code: 1981BAAS...13..881S
Abstract
@--------------------------------------------------------------------
Title: Gyrosynchrotron Masering in Solar Flares
Authors: Morrison, P. J.; Holman, G. D.; Kundu, M. R.
Bibliographic Code: 1981BAAS...13..860M
Abstract
@--------------------------------------------------------------------
Title: A Search for Microwave Counterparts of Umbral
Flashes
Authors: McConnell, D.; Kundu, M. R.; Schmahl, E. J.;
Lites, B.
Bibliographic Code: 1981BAAS...13..858M
Abstract
@--------------------------------------------------------------------
Title: Flare Buildup at 6 cm Wavelength, in UV and Halpha
Authors: Schmahl, E. J.; Kundu, M. R.; Woodgate, B.;
Shine, R.
Bibliographic Code: 1981BAAS...13..846S
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of Large Scale Microwave
Brightening Following a Flare
Authors: Bobrowsky, M.; Kundu, M. R.; Rust, D.
Bibliographic Code: 1981BAAS...13..846B
Abstract
@--------------------------------------------------------------------
Title: Interpretation of Microwave and X-Ray Bursts
Observed with the VLA and P78-1
Authors: Schmahl, E. J.; Kundu, M. R.; Landecker, P. B.;
McKenzie, D. L.
Bibliographic Code: 1981BAAS...13..553S
Abstract
@--------------------------------------------------------------------
Title: Microwave solar limb brightening
Authors: Ahmad, I. A.; Kundu, M. R.
Bibliographic Code: 1981SoPh...69..273A
Abstract
Previous models of microwave limb brightening have omitted the alignment
of spicules along supergranule boundaries, have neglected the high
temperature sheath around spicules, and have assumed an interspicular
medium which was averaged over chromospheric network and nonnetwork
regions. A model is presented here which includes these factors.
Constraining the model to conform to results from earlier UV and optical
studies in effect leaves two free parameters: the temperature at the
core of the spicules and (at solar minimum) the interspicular
chromospheric network density model of the lower transition zone. The
absence of limb brightening at the short millimeter wavelengths implies
a temperature at the core of the spicules less than approximately 6000
K. Differences between the model and certain deconvolved observations
near 9 mm are expected as a consequence of an extension of emission
beyond the optical limb, predicted by the model, which affects the
accuracy of the deconvolution technique. Unlike models which assume
homogeneous spicules in a random distribution, the model presented here
does not require an abnormally high spicule area.
@--------------------------------------------------------------------
Title: A Multifrequency Study of CTB:80 with the Westerbork
Synthesis Radio Telescope
Authors: Angerhofer, P. E.; Strom, R. G.; Velusamy, T.;
Kundu, M. R.
Bibliographic Code: 1981A&A....94..313A
Abstract
We report observations of the galactic supernova remnant CTB 80 (W56,
G69.0 +2.7) with the Westerbork Synthesis Radio Telescope (WSRT) at 6,
2t, and 49 cm wavelengths. Maps of the brightness distribution and
linear polarization are presented for each wavelength, along with
discussion of the distributions of spectral index, magnetic field
direction and rotation measure over the central source and radio ridges.
The new data suggest that the bright central source and the extended
underlying emission are physically associated. The spectrum over the
central source is flat (alpha ˜ 0.0), steepening uniformly away
from the core in all directions. Linear polarization is detected at all
three observed wavelengths. The morphology, high degree of polarization
and flat spectral index of the core suggest that `the central source may
belong to the Crab Nebula type SNR class.
Inspection of the PSS plates reveals the presence of considerable
optical nebulosity at the position of the radio continuum peak, adding
CTB 80 to the list of ˜30 optically visible supernova remnants.
@--------------------------------------------------------------------
Title: VLA observations of postflare loops at 20 centimeter
wavelength
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1981ApJ...243L.103V
Abstract
From observations with the VLA on May 19, 1979, the first spatially
resolved observations of 20 cm radio emission originating from postflare
loop systems are presented. The 20 cm burst was associated with an H
alpha flare and a soft X-ray burst, and most of the intense radio
emission occurred at the end of the H alpha flare and in the decay phase
of the X-ray burst. The 20 cm 'snapshot' maps of the burst source
obtained with a resolution of 12 arcsec x 24 arcsec show that the radio
emission occurred in structures that are similar in size and shape to
the systems of loops observed in X-rays. This postflare radio emission
is considered to be similar to the H alpha and X-ray emissions
originating in postflare loops. The radio observations of postflare
loops have the unique advantage that they offer an important means of
determining the average magnetic field strength in these loops.
Interpreting the radio emission in this particular event as thermal
gyroradiation or as nonthermal synchrotron radiation, the magnetic field
strength is estimated to lie in the range of approximately 120-170
gauss.
@--------------------------------------------------------------------
Title: VLA observations of solar active regions at 6 CM
wavelength
Authors: Kundu, M. R.; Schmahl, E. J.; Rao, A. P.
Bibliographic Code: 1981A&A....94...72K
Abstract
Synthesized maps of two solar active regions obtained from observations
with the Very Large Array (VLA) with 9-arcsec resolution are presented.
The most intense sources in these regions are found to be associated
with filamentary structures and magnetic neutral lines as shown in
H-alpha and photospheric magnetograms. These sources are not located
directly over sunspots in disagreement with earlier observations. EUV
and X-ray observations have suggested that similar structures should be
visible at cm wavelengths around but, outside of, sunspots if the
magnetic field is sufficiently strong. These results are consistent with
the locations of hot (greater than 1,000,000 K) plasmas in active
regions expected from generalization based on optical photographs. Given
the sizes of the radio sources, the volume emission measures of soft
X-rays observed from OSO-8 rule out the possibility of thermal
bremsstrahlung being of any significance, as far as the 6 cm emission is
concerned. Therefore, gyroresonance absorption process is the most
likely cause of 6 cm emission from these sources, and its likelihood is
enhanced by the magnetic field geometry that is known to exist over
filaments and neutral lines.
@--------------------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun
Authors: Kundu, M. R.; Gergely, T. E.; Maxwell, A.
Bibliographic Code: 1981S&T....62..149K
Abstract
@--------------------------------------------------------------------
Title: Observing the Sun during Eclipses
Authors: Kundu, M. R.
Bibliographic Code: 1981Mercu..10..108K
Abstract
@--------------------------------------------------------------------
Title: Observations of the old supernova remnant S 147 at
11.1 and 18.2 CM wavelengths
Authors: Kundu, M. R.; Angerhofer, P. E.; Fuerst, E.;
Hirth, W.
Bibliographic Code: 1980A&A....92..225K
Abstract
New high resolution and high sensitivity radio observations of the old
galactic supernova remnant S 147, made at wavelengths of 11.1 and 18.2
cm, are reported. The data reveal the presence of a well developed radio
shell. The integrated flux density spectrum shows a distinct break at 1
GHz, attributed to enhanced volume emissivity of the swept-up
interstellar material. The age of S 147 is likely to be about 100,000
yr, making it one of the oldest optically visible supernova remnants in
the Galaxy. Derived physical parameters, based on the new data, are also
reported.
@--------------------------------------------------------------------
Title: Erratum - MICROWAVE_ EUV and X-Ray Observations of
Active Region Loops - Evidence for Gyroresonance
Absorption in the Corona
Authors: Kundu, M. R.; Schmahl, E. J.; Gerassimenko, M.
Bibliographic Code: 1980A&A....91..377K
Abstract
@--------------------------------------------------------------------
Title: Upper limits on the power in solar oscillations at
1.2 mm, 9 mm, 3.7 cm, and 11.1 CM wavelengths
Authors: Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1980A&A....90..192K
Abstract
A search for solar oscillations has been made using the NRAO 36-ft
telescope at 1.2 mm, the NRL 85-ft telescope at 9 mm, and the NRAO
four-element interferometer at 3.7 and 11.1 cm wavelengths. After
corrections for the small coherence length of the optically observed
oscillations, for their known spectral bandwidth, and for the visibility
function of the interferometer, upper limits have been placed on the
fluctuating power at oscillation frequencies near 3 mHz. The
interferometric observations at 3.7 cm and the single-dish observations
at 1.2 and 9 mm imply that less than 0.3, 0.04, and 0.1%, respectively,
of the bremsstrahlung photons emitted from the chromosphere show
periodic fluctuations. This is 1 to 3 orders of magnitude less than the
fraction (approximately 1 to 2%) reported at ultraviolet wavelengths.
Simple arguments in terms of weak shock theory suggest that the
observable oscillations at centimeter and millimeter wavelengths should
be intrinsically weaker in the thermal bremmstrahlung radiation than the
optical, but the 3.7 cm wavelength results are explained only by the
absence of periodic fluctuations at the level of formation.
@--------------------------------------------------------------------
Title: Comparison of VLA Microwave Maps of Active Regions
with X-ray Spectroheliograms
Authors: Schmahl, E. J.; Kundu, M. R.; Strong, K. T.
Bibliographic Code: 1980BAAS...12Q.907S
Abstract
@--------------------------------------------------------------------
Title: Correlated Soft X-Ray and Microwave Observations of
Active Region Loops
Authors: Webb, D. F.; Davis, J. M.; Kundu, M. R.;
Velusamy, T.
Bibliographic Code: 1980BAAS...12..916W
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of a Centimeter Wavelength Burst
Associated With a Filament Eruption on May 14, 1980
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1980BAAS...12..901V
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of the Impulsive Phase of the June
25, 1980 Flare at 6 CM Wavelength
Authors: Kundu, M. R.; Velusamy, T.; Schmahl, E. J.
Bibliographic Code: 1980BAAS...12..901K
Abstract
@--------------------------------------------------------------------
Title: Nonthermal Flare Emission and the Nonlinear Dynamics
of High Energy Electrons
Authors: Holman, G. D.; Papadopoulos, K.; Kundu, M. R.
Bibliographic Code: 1980BAAS...12..901H
Abstract
@--------------------------------------------------------------------
Title: VLA Observations of Two SMM Flares at 6 cm
Authors: Erskine, F. T.; Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1980BAAS...12..901E
Abstract
@--------------------------------------------------------------------
Title: Radio and Visible Light Observations of a Coronal
Transient Associated with a Prominence Eruption
Authors: Gergely, T. E.; Kundu, M. R.; Erskine, F. T.;
Sawyer, C.; Wagner, W. J.; Illing, R.; House, L. L.;
McCabe, M. K.; Stewart, R. T.; Nelson, G. J.
Bibliographic Code: 1980BAAS...12..900G
Abstract
@--------------------------------------------------------------------
Title: Observation with the VLA of a stationary loop
structure on the sun at 6 centimeter wavelength
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1980ApJ...240L..63K
Abstract
A looplike structure connecting two sunspots of opposite polarity in an
active region has been observed at 6 cm with a resolution of 3.5 arcsec,
using the Very Large Array. This loop structure is reminiscent of the
X-ray loops, as observed, for example, from Skylab. The brightness
temperature in the 'loop' is one-million K and five-million K near its
foot points. Most of the bright peaks in the 'loop' are well aligned
with a long neutral line. Several compact, highly circularly polarized
emission peaks were observed over emerging flux regions near one of the
spots. Some of these sources appear to be associated with arch filament
systems. The low brightness emission in the 'loop' is attributed to
optically thin thermal bremsstrahlung.
@--------------------------------------------------------------------
Title: Synthesized map of a solar filament at 6 CM with
approximately 15 arc SEC resolution
Authors: Rao, A. P.; Kundu, M. R.
Bibliographic Code: 1980A&A....86..373R
Abstract
Radio telescope observations have been used to provide the first
synthesized map of a filament at 6 cm with angular resolution of about
15 arcsec. The 'dirty' map of the north limb of the sun is shown along
with the dirty map of the residual after subtracting the three component
least squares model. There is very good correspondence between the radio
contours and the H alpha filament; the darkest feature of the filament
has a radio temperature depression of 7500 plus or minus 1500 K, and the
corresponding brightness temperature of the filament is 12500 plus or
minus 1500 K. It is concluded that for this particular filament the
radio size is not larger than the optical one.
@--------------------------------------------------------------------
Title: Observation with the VLA of a Stationary Loop
Structure on the Sun at 6 cm Wavelength
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1980BAAS...12..519K
Abstract
@--------------------------------------------------------------------
Title: Thermal Radio Emission from Solar Active Regions
Authors: Holman, G. D.; Kundu, M. R.
Bibliographic Code: 1980BAAS...12..517H
Abstract
@--------------------------------------------------------------------
Title: Observations of Solar Filaments at 8, 15, 22, and 43
Ghz
Authors: Schmahl, E. J.; Bobrowsky, M.; Kundu, M. R.
Bibliographic Code: 1980BAAS...12..507S
Abstract
@--------------------------------------------------------------------
Title: Time Variability and Structure of Quiet Sun Sources
at 6 cm Wavelength
Authors: Erskine, F. T.; Kundu, M. R.
Bibliographic Code: 1980BAAS...12..504E
Abstract
@--------------------------------------------------------------------
Title: Two-Dimensional Snapshot Maps with the VLA of a
Solar Burst at 20 cm Wavelength
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1980BAAS...12..478V
Abstract
@--------------------------------------------------------------------
Title: Nature of Meter-Decameter Bursts Associated with
Hard X-ray Bursts
Authors: Kundu, M. R.; Gergely, T. E.; Kane, S. R.
Bibliographic Code: 1980BAAS...12..478K
Abstract
@--------------------------------------------------------------------
Title: Association of flaring X-ray bright points with type
III bursts
Authors: Kundu, M. R.; Gergely, T. E.; Golub, L.
Bibliographic Code: 1980ApJ...236L..87K
Abstract
Using the swept-frequency radio observations obtained at the Clark Lake
Radio Observatory and the X-ray photographs taken by the S-054
experiment aboard Skylab, a search has been made for type III bursts
associated with X-ray bright point (XBP) flares. Using temporal as well
as spatial criteria for the association, four such events are found over
a period of 43 days. The time period was selected in such a way that the
level of flare and radio activity was low in order to minimize the
chance coincidences. The detection of type III bursts from the flaring
XBPs is of great interest, since it identifies them with the flare
process, of which XBP flares are thought to be the simplest form.
@--------------------------------------------------------------------
Title: 6 CM observations of a solar active region and
bursts with approximately 6 arcsec resolution
Authors: Erskine, F. T.; Kundu, M. R.; Rao, A. P.
Bibliographic Code: 1980A&A....83..256E
Abstract
The paper examines the solar active region located near N04E49, that was
mapped at a 6 cm wavelength over a period of 12 hours, employing the
Westerbork synthesis radio telescope. Two impulsive radio bursts were
recorded during this time, one of which was associated with a
chromospheric flare. One-dimensional fan beam scans of the burst sources
were synthesized in order to display their time history with regard to
intensity, polarization, position and size.
@--------------------------------------------------------------------
Title: Microwave, EUV, and X-ray observations of active
region loops - Evidence for gyroresonance absorption
in the corona [ Erratum: 1980A&A....91..377K ]
Authors: Kundu, M. R.; Schmahl, E. J.; Gerassimenko, M.
Bibliographic Code: 1980A&A....82..265K
Abstract
The combined data from 3.7 and 11 cm radio maps, EUV spectroheliograms,
and X-ray photographs of an active region (McMath 12379) are analyzed.
The near equality of the radio brightness temperatures and the electron
temperature determined from the EUV and X-ray data implies that the
radio emission is thermal. Since the free-free absorption is inadequate
to account for this, the large optical depth must be produced by
gyroresonance absorption. It is inferred that the magnetic scale height
must be of the same order as the observed width of the coronal loops
(one-billion cm). The scale of emission in the radio, and hence the
scale of the absorbing region transverse to the line of sight, is also
of this order.
@--------------------------------------------------------------------
Title: A model for sunspot associated emission at 6 CM
wavelength
Authors: Alissandrakis, C. E.; Kundu, M. R.; Lantos, P.
Bibliographic Code: 1980A&A....82...30A
Abstract
Two-dimensional maps of total intensity and circular polarization of a
sunspot region at 6 cm have been calculated using a simple model for the
chromosphere-corona transition region and observations of the
longitudinal component of the photospheric magnetic field. The
calculations are in good agreement with the high resolution observations
of the same sunspot region at 6 cm, obtained with the Westerbork
Synthesis Radio Telescope. It is shown that the 6 cm radiation is
predominantly due to gyroresonance absorption process at the second and
third harmonics of the gyrofrequency (H = 900-600 G). Estimates of the
conductive flux and the electron density in the transition region above
the sunspot are also given.
@--------------------------------------------------------------------
Title: Maryland, University of
Authors: Kundu, M. R.
Bibliographic Code: 1980BAAS...12..226K
Abstract
@--------------------------------------------------------------------
Title: Impulsive phase of solar flares
Authors: Kane, S. R.; Crannell, C. J.; Datlowe, D.;
Feldman, U.; Gabriel, A.; Hudson, H. S.;
Kundu, M. R.; Maetzler, C.; Neidig, D.;
Petrosian, V.
Bibliographic Code: 1980sfsl.work..187K
Abstract
The present understanding of the impulsive phase of a solar flare,
characterized by short-duration bursts of impulsive hard X-ray, EUV,
optical and radio emission indicating the release of energetic electrons
is reviewed. Observations of the spectral distribution of impulsive hard
X-ray bursts and of Type III and radio continuum bursts are presented
and interpreted in terms of energetic electron distributions, and
impulsive EUV, XUV, soft X-ray and optical observations, which provide a
lower limit to total energy release during the impulsive phase, are
discussed. The role of energetic electrons in exciting the hard X-ray,
EUV and microwave emissions is considered, and thin-target,
thick-target, partial-precipitation and thermal models of impulsive
phase electron acceleration are evaluated in light of the observations.
It is noted that available data do not allow discrimination between a
thermal or a nonthermal electron distribution, on which depends the
proportion of flare energy supplied by the energetic electrons, and that
data favors models which permit at least partial electron precipitation.
Future observational and theoretical work is indicated.
@--------------------------------------------------------------------
Title: Book-Review - Radio Physics of the Sun IAU Symp 86
Authors: Kundu, M. R.; Gergely, T. E.
Bibliographic Code: 1980Natur.287..373K
Abstract
@--------------------------------------------------------------------
Title: Decameter radio and white light observations of the
21 August 1973 coronal transient
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1980IAUS...91..245G
Abstract
The forces driving the ejecta of the coronal transient of August 21,
1973 are estimated using physical parameters derived by joint radio and
white light observations. The radio emission associated with the
transient was continuum in nature, and lasted for almost 5 hours.
Simultaneous radio and white light measurements show that the radio
source was cospatial with one of the secondary white light loops.
Assuming a coronal temperature of 1,500,000 K, the results yield an
approximate equality of the gas and magnetic pressures at 2.0 solar
radii. It is concluded that for this transient, the gas is strongly
influenced by changes in the magnetic field.
@--------------------------------------------------------------------
Title: An interpretation of solar flare microwave spikes as
gyrosynchrotron masering
Authors: Holman, G. D.; Eichler, D.; Kundu, M. R.
Bibliographic Code: 1980IAUS...86..457H
Abstract
@--------------------------------------------------------------------
Title: Decametric radio bursts associated with coronal loop
structures
Authors: Gergely, T. E.; Kundu, M. R.; Golub, L.; Webb, D.
Bibliographic Code: 1980IAUS...86..435G
Abstract
The association of X-ray loop structures with type III bursts is
examined using soft X-ray (2-54 A) pictures which were obtained from the
Skylab S-054 experiment. The properties of meter-decameter wavelength
radio bursts (type III) appear to be associated with two different kinds
of loop structures: (1) short lived small scale loops, which are found
to link magnetic fields of opposite polarity, called X-ray bright points
(XBP); and (2) long lasting loop systems which connect opposite magnetic
polarities of an active region as well as active region complexes. It is
judged that the presence of active region loop complexes on the disk is
a necessary yet insufficient condition for the occurrence of a
decametric storm and that conditions concerning the geometry of the
magnetic field must also be important in the process.
@--------------------------------------------------------------------
Title: Solar burst observations at centimeter wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1980IAUS...86..157K
Abstract
Selected features of centimeter-wave solar radio burst are discussed in
relation to the generating mechanism of these bursts. Observations are
presented of active regions prior to the onset of a flare, the intensity
distributions of flares, the impulsive phase of a burst, the post-burst
phase, and gradual rise and fall burst. Analysis of high-resolution
impulsive bursts leads to a model of burst emission in which impulsively
accelerated plasma contained within loop structures is responsible for
the impulsive burst phase by the ejection of high energy particles and
for the post-burst phase by the spread of slower particles, with
emission in the centimeter wave region primarily by bremsstrahlung. It
is also pointed out that the impulsive centimeter-wave bursts have been
found to correspond with hard X-ray bursts as well as soft X-ray
kernels, indicating that the centimeter wave region is no larger than
the X-ray emitting region, which would require either self-absorption or
an asymmetrical bipolar field structure to explain the greater X-ray
intensities.
@--------------------------------------------------------------------
Title: Observations of solar active regions at 2 and 6 CM
wavelengths with 3 arc second resolution
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1980IAUS...86..105V
Abstract
@--------------------------------------------------------------------
Title: Observations of the quiet sun with 6 arcsec
resolution
Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.;
Bregman, J. D.
Bibliographic Code: 1980IAUS...86...53K
Abstract
High-resolution observations of the quiet sun at 6 cm are reported. The
Westerbork Synthesis Radio Telescope was used to observe a central 10 x
10 arcmin disk region for 12 hours at a resolution of 6 arcsec in the
E-W direction and 15 arcsec in the N-S direction. The resulting radio
map reveals the presence of a supergranulation network with network
elements of 25,000 K and cells of 15,000 K, and which is of the same
scale as the Ca(+) network. Sequential observations of the north, south,
east and west limbs reveal a limb brightening of 40-60% above the mean
disk temperature, the peak of which is located 15 arcsec outside the
optical disk.
@--------------------------------------------------------------------
Title: Radio physics of the sun; Proceedings of the
Symposium, University of Maryland, College Park,
Md., August 7-10, 1979
Authors: Kundu, M. R.; Gergely, T. E.
Bibliographic Code: 1980IAUS...86.....K
Abstract
Papers are presented in the areas of the radio characteristics of the
quiet sun and active regions, the centimeter, meter and decameter
wavelength characteristics of solar bursts, space observations of
low-frequency bursts, theoretical interpretations of solar active
regions and bursts, joint radio, visual and X-ray observations of active
regions and bursts, and the similarities of stellar radio
characteristics to solar radio phenomena. Specific topics include the
centimeter and millimeter wave characteristics of the quiet sun, radio
fluctuations arising upon the transit of shock waves through the
transition region, microwave, EUV and X-ray observations of active
region loops and filaments, interferometric observations of 35-GHz radio
bursts, emission mechanisms for radio bursts, the spatial structure of
microwave bursts, observations of type III bursts, the statistics of
type I bursts, and the numerical simulation of type III bursts.
Attention is also given to the theory of type IV decimeter bursts,
Voyager observations of type II and III bursts at kilometric
wavelengths, radio and whitelight observations of coronal transients,
and the possibility of obtaining radio observations of current sheets on
the sun.
@--------------------------------------------------------------------
Title: Centimeter Wavelength Observations of Solar Active
Regions With The Very Large Array
Authors: Kundu, M. R.; Schmahl, E. J.; Rao, A. P.
Bibliographic Code: 1979BAAS...11R.710K
Abstract
@--------------------------------------------------------------------
Title: Upper Limits on Solar Oscillation Power in
Microwaves
Authors: Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1979BAAS...11..641K
Abstract
@--------------------------------------------------------------------
Title: High-resolution observations of the quiet sun at 6
centimeters using the Westerbork Synthesis Radio
Telescope
Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.;
Bregman, J. D.
Bibliographic Code: 1979ApJ...234.1122K
Abstract
High-spatial-resolution (~6") observations of the quiet Sun were
made at 6 cm with the Westerbork Synthesis Radio Telescope. A 10'
× 10' field of the central disk region observed on 1976 June 16
was synthesized. We show the first radio map of the supergranulation
network. Numerical autocorrelation of the radio map indicated a radio
"network" width ~11,000 km and a radio "cell" spacing ~32,000
km. The brightness temperature of typical network elements is ~2.5
× l04 K, while that of the radio cells is ~1.5
× l04 K. The contrast between the radio network and
cells is ~1.7:1 which is intermediate to that of the
Ca+ K network and Lalpha network. The radio map was
compared with a Ca+ K spectroheliogram of the same region
on the same day. On 1976 June 17, the four limbs of the Sun were also
observed in an attempt to synthesize the limb and study the extent and
symmetry of limb brightening. The results show that limb brightening
is seen both in the north-south and east-west directions, contrary to
earlier low-resolution measurements which showed limb brightening only
in the east-west direction. The peak of the limb brightening appears
~15" outside the white-light disk and the peak limb temperature is
~40% greater than the mean disk temperature.
@--------------------------------------------------------------------
Title: Radio interferometric observations of solar bursts
at 3.7 and 11.1 CM wavelengths
Authors: Kundu, M. R.; Angerhofer, P. E.
Bibliographic Code: 1979SoPh...64..159K
Abstract
Several solar active regions were observed during the 1976 vernal
equinox with the 3-element interferometer of the National Radio
Astronomy Observatory. The element spacings for these observations
were 600,2100, and 2700 m, resulting in maximum angular resolutions of
about 3 arc sec at 3.7 cm and 8.5 arc sec at 11.1 cm. We fitted the
fringe visibility for each baseline pair as a function of projected
baseline with a single gaussian component, and calculated the
extrapolated flux at zero baseline, F0, the FWHM source
size, a, and the peak brightness temperature Tb. We present
physical parameters derived for the observed bursts.
@--------------------------------------------------------------------
Title: An interpretation of the polarization of microwave
bursts
Authors: Kundu, M. R.; Vlahos, L.
Bibliographic Code: 1979ApJ...232..595K
Abstract
High-spatial-resolution (a few seconds of arc) observations of microwave
bursts have demonstrated that only the impulsive phase of the burst is
polarized; one observes only one polarity in the burst source if it is
weak (Alissandrakis and Kundu) and both polarities if it is intense
(Enome et al.). These results are interpreted in terms of an
asymmetrical bipolar field structure of the loop in which the energetic
electrons responsible for the radiation are contained. The role of
unequal field strengths at the feet of the loop on the number of
electrons trapped and their pitch angle distribution are discussed in a
specific model. Computations of the polarized intensity originating from
each foot of the loop seem to be consistent with the observations at
present available.
@--------------------------------------------------------------------
Title: Radio and white-light observations of the 1973
August 21 coronal transient
Authors: Gergely, T. E.; Kundu, M. R.; Munro, R. H.;
Poland, A. I.
Bibliographic Code: 1979ApJ...230..575G
Abstract
A coronal transient, which occurred on August 21, 1973, has been
observed simultaneously in white light and at decameter radio
wavelengths. The radio observations were obtained with a two-dimensional
swept-frequency array (called the Teepee Tee). The white-light
observations consist of a series of photographs taken by the High
Altitude Observatory's coronagraph aboard Skylab. The radio emission
associated with the transient was continuum in nature and lasted for
almost 5 hours. The source of emission was observed to be cospatial with
the lower part of one of the secondary white-light loops. A lower limit
of 0.6 solar radius for the depth (extension along the line of sight) of
this part of the transient was derived from considerations of radio-wave
propagation in the corona. The radio source showed no dispersion of
height with frequency, and, therefore, the emission is attributed to
gyrosynchrotron radiation. Based on this assumption, the magnetic-field
strength in the lower part of the loop is estimated to be in the
2.0-4.5-gauss range at a height of 2.1 solar radii from the center of
the sun.
@--------------------------------------------------------------------
Title: Observations of Alpha Orionis, R Aquilae, and R
Aquarii at 14.9 GHz
Authors: Bowers, P. F.; Kundu, M. R.
Bibliographic Code: 1979AJ.....84..791B
Abstract
The 14.9-GHz continuum flux densities of the M-type stars Alpha Ori, R
Aql, and R Aqr have been measured. For Alpha Ori and R Aql it is
suggested that the emission at this frequency is primarily due to
ionized gas associated with stellar chromospheres or coronae. For R Aqr
a model consistent with available data is proposed in which the variable
intensity of the radio emission depends on a variable mass-loss rate for
the Mira.
@--------------------------------------------------------------------
Title: Solar Atmospheric Inhomogeneities and Limb
Brightening Models
Authors: Ahmad, I. A.; Kundu, M. R.
Bibliographic Code: 1979BAAS...11..410A
Abstract
@--------------------------------------------------------------------
Title: A broad look at solar physics adapted from the solar
physics study of August 1975
Authors: Parker, E.; Timothy, A.; Beckers, J.; Hundhausen, A.;
Kundu, M. R.; Leith, C. E.; Lin, R.; Linsky, J.;
MacDonald, F. B.; Noyes, R.
Bibliographic Code: 1979sswp.book....3P
Abstract
The current status of our knowledge of the basic mechanisms involved in
fundamental solar phenomena is reviewed. These include mechanisms
responsible for heating the corona, the generation of the solar wind,
the particle acceleration in flares, and the dissipation of magnetic
energy in field reversal regions, known as current sheets. The
discussion covers solar flares and high-energy phenomena, solar active
regions; solar interior, convection, and activity; the structure and
energetics of the quiet solar atmosphere; the structure of the corona;
the solar composition; and solar terrestrial interactions. It also
covers a program of solar research, including the special observational
requirements for spectral and angular resolution, sensitivity, time
resolution, and duration of the techniques employed.
@--------------------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Kundu, M. R.; Maltby, P.; Malville, J.;
Orrall, F. Q.; Sheeley, N.; Spicer, D. S.
Bibliographic Code: 1979phsp.coll..225A
Abstract
@--------------------------------------------------------------------
Title: Discussion
Authors: Chiuderi-Drago, F.; Kundu, M. R.; Lantos, P.;
Zirin, H.
Bibliographic Code: 1979phsp.coll..134C
Abstract
@--------------------------------------------------------------------
Title: Discussion
Authors: Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1979phsp.coll..129K
Abstract
@--------------------------------------------------------------------
Title: Observations of filaments at centimeter and
millimeter wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1979phsp.coll..122K
Abstract
Observations of quiescent-prominence radio filaments at centimeter and
millimeter wavelengths are reviewed. The finding that a radio filament
appears cooler than the background quiet sun is interpreted by
postulating that the filament is cool and optically thick, in which case
the brightness temperature of the filament should be the same as its
kinetic temperature. Optical spectroscopic observations are discussed
which indicate that a typical filament has an electron density of
approximately 100 billion per cu cm, a temperature of about 6000 K, and
a length of approximately 1000 km, implying that the optical thickness
is much greater than unity for all frequencies less than 600 GHz.
Millimeter- and centimeter-wavelength observations of filaments at the
limb are shown also to support the view that the filaments are optically
thick at these wavelengths. Radio observations of filament transition
sheaths and cavities are also examined.
@--------------------------------------------------------------------
Title: Discussion
Authors: Landi Degl'Innocenti, M.; Kundu, M. R.;
Landman, D. A.; Smartt, R. N.; Stenflo, J.
Bibliographic Code: 1979phsp.coll...85L
Abstract
@--------------------------------------------------------------------
Title: Discussion
Authors: Anzer, U.; Chiuderi-Drago, F.; Kundu, M. R.;
Leroy, J. L.; Malville, J.; Rompolt, B.; Sheeley, N.;
Stenflo, J.; Tandberg-Hanssen, E.; Öhman, Y.
Bibliographic Code: 1979phsp.coll...77A
Abstract
@--------------------------------------------------------------------
Title: Discussion
Authors: Acton, L. W.; Engvold, O.; Heasley, J. N.;
Heyvaerts, J.; Hirayama, T.; Kundu, M. R.;
Leroy, J. L.; Malville, J.; Rust, D. M.; Zirin, H.
Bibliographic Code: 1979phsp.coll...31A
Abstract
@--------------------------------------------------------------------
Title: Radiobeobachtungen an S 147, ein Beitrag zur
Diskussion alter Supernovaüberreste
Authors: Fürst, E.; Hirth, W.; Angerhofer, P. E.;
Kundu, M. R.; Sofue, Y.
Bibliographic Code: 1979MitAG..45..103F
Abstract
@--------------------------------------------------------------------
Title: Comparison of radio and EUV filaments: a
two-component model.
Authors: Kundu, M. R.; Schmahl, E. J.
Bibliographic Code: 1979BAAS...11..393K
Abstract
@--------------------------------------------------------------------
Title: Fine structure and time variation of the quiet sun
at 1.3 CM
Authors: Rao, A. P.; Kundu, M. R.
Bibliographic Code: 1978SoPh...59..345R
Abstract
The Hat Creek two-element interferometer has been used to study the
quiet sun at 22 GHz. A statistical analysis of output of the
interferometer clearly shows the existence of time variations on the
quiet sun with time scales of approximately 180 s. The observations
suggest that the fine structure on the quiet sun might consist of two
components - one which varies with the time scales of approximately 3
min and the other being relatively stable. The average visibility
amplitude indicates that the fine structure on the sun has a typical
angular size of approximately 6 sec. The observation that the variance
and the mean of the visibility amplitudes depend in the same way on the
projected baseline suggests that the transient sources have angular size
similar to the average size of the fine structure on the quiet sun.
Power spectra of the output of the interferometer show no significant
periodicity.
@--------------------------------------------------------------------
Title: Decameter Radio Observations of the 5 September,
1973 Flare
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1978BAAS...10R.672G
Abstract
@--------------------------------------------------------------------
Title: High Resolution Observations of the Quiet Sun at 6
cm Using the Westerbork Synthesis Radio Telescope
Authors: Kundu, M. R.; Rao, A. P.; Erskine, F. T.;
Bregman, J. D.
Bibliographic Code: 1978BAAS...10Q.686K
Abstract
@--------------------------------------------------------------------
Title: High resolution observations of CTB 80 at 6.21 and
50 centimetres.
Authors: Velusamy, T.; Angerhofer, P.; Kundu, M. R.;
Storm, R.
Bibliographic Code: 1978BASI....6...53V
Abstract
@--------------------------------------------------------------------
Title: 6 centimeter observations of solar bursts with
6-inch resolution
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1978ApJ...222..342A
Abstract
During May 1974 data were collected on nine 6-cm solar bursts
originating in two active regions. One-dimensional fan-beam scans were
obtained every 30 seconds in order to study burst structure and
evolution. Maximum burst flux was in the 0.34-12.0 sfu range. At maximum
intensity the estimated brightness temperatures were in the 10 to the
6th to 2 x 10 to the 7th K range. Angular sizes ranged from 7-23 arcsec.
In most cases an expansion of the burst core after maximum intensity was
observed along with a drift in the position of the burst core. Four
bursts were associated important H-alpha flares, and in all cases burst
maximum occurred before flare maximum. The bursts were circularly
polarized in the extraordinary mode sense during maximum intensity.
Since the polarization was the same over the extent of the burst source,
it is suggested that if the burst is associated with loop sources, the
emission is associated with one leg of the loop.
@--------------------------------------------------------------------
Title: The association of nonthermal electrons with
non-flaring coronal transients
Authors: Webb, D. F.; Kundu, M. R.
Bibliographic Code: 1978SoPh...57..155W
Abstract
A close temporal and spatial association has been found between erupting
filaments/coronal transients and radio noise storm continua. The three
transients studied occurred away from active regions and are members of
a class not usually accompanied by chromospheric emission. The data
analyzed were from the S-054 soft X-ray telescope on Skylab and from
one- and two-dimensional interferometers at meter and decameter
wavelengths at Nancay and Clark Lake observatories. Calculations
confirmed that observed microwave radiation from the transients is due
to thermal bremsstrahlung. The results are consistent with an
interpretation of heating of an increased amount of coronal plasma by
nonthermal, 10-100 keV electrons. Three possibilities for the source of
the material are described: (1) the filament material; (2) evaporation
from the chromosphere or transition region; and (3) via a long-lived
reconnection process.
@--------------------------------------------------------------------
Title: Radio and White Light Observations of the 21 August
1973 Coronal Transient.
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1978BAAS...10..456G
Abstract
@--------------------------------------------------------------------
Title: Possible Explanation for the turnovers in Two Solar
Microwave Burst Spectra.
Authors: Ahmad, I. W.; Kundu, M. R.
Bibliographic Code: 1978BAAS...10..455A
Abstract
@--------------------------------------------------------------------
Title: Fine Structure and Time Variation of the Quiet Sun
at 1.3 cm.
Authors: Rao, A. P.; Kundu, M. R.
Bibliographic Code: 1978BAAS...10..431R
Abstract
@--------------------------------------------------------------------
Title: Radio Interferometric Observations of the Bright
Core of CTB 80.
Authors: Angerhofer, P. E.; Kundu, M. R.
Bibliographic Code: 1978BAAS...10..427A
Abstract
@--------------------------------------------------------------------
Title: Multifrequency observations of solar filaments at
centimeter wavelengths
Authors: Kundu, M. R.; Fuerst, E.; Hirth, W.; Butz, M.
Bibliographic Code: 1978A&A....62..431K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1978A&A....62..431K
@--------------------------------------------------------------------
Title: A study of filament transition sheath from radio
observations
Authors: Rao, A. P.; Kundu, M. R.
Bibliographic Code: 1977SoPh...55..161R
Abstract
An H-alpha dark filament has been observed at 8, 15 and 22 GHz, and its
radio spectrum derived. It is suggested that the filament may be
optically thick at radio frequencies and that the observed spectrum may
be due to the presence of a transition sheath surrounding the filament.
A model is developed for the transition sheath in which the energy
radiated away is balanced by the conduction of heat from the corona; the
radio observations indicate that little or no thermal energy is
conducted into the main body of the filament. The model is compared with
ultraviolet observations of filaments.
@--------------------------------------------------------------------
Title: 2.8 and 6 CM wavelength observations of NGC 7822
Authors: Angerhofer, P. E.; Kundu, M. R.; Becker, R. H.;
Velusamy, T.
Bibliographic Code: 1977A&A....61..285A
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1977A&A....61..285A
@--------------------------------------------------------------------
Title: Determination of the decameter wavelength spectrum
of the quiet sun
Authors: Erickson, W. C.; Kundu, M. R.; Mahoney, M. J.;
Gergely, T. E.
Bibliographic Code: 1977SoPh...54...57E
Abstract
The Teepee Tee array of the Clark Lake Radio Observatory has been used
to compare the flux of the Sun with that of the sidereal sources Tau A
and Vir A at several frequencies in the range 109.0-19.0 MHz. Only the
two central banks of the E-W arm of the array were used as elements of a
phase switched interferometer so that the Sun could be observed as a
point source and compared directly to the sidereal sources. The Sun was
still partially resolved however, and appropriate corrections for this
effect were made. The observations were taken at times when the Sun and
either Tau A or Vir A were at the same declination. We have therefore
been able to derive the values for the solar flux, without having to
resort to a gain vs zenith distance correction. The observations,
combined with those available in the literature, allow us to derive an
accurate meter and decameter wavelength spectrum of the quiet Sun.
@--------------------------------------------------------------------
Title: Coordinated X-ray, optical, and radio observations
of YZ Canis Minoris
Authors: Karpen, J. T.; Crannell, C. J.; Hobbs, R. W.;
Maran, S. P.; Moffett, T. J.; Bardas, D.;
Clark, G. W.; Hearn, D. R.; Li, F. K.;
Markert, T. H.; McClintock, J. E.; Primini, F. A.;
Richardson, J. A.; Cristaldi, S.; Rodono, M.;
Galasso, D. A.; Magun, A.; Nelson, G. J.;
Slee, O. B.; Chugainov, P. F.; Efimov, Yu. S.;
Shakhovskoy, N. M.; Viner, M. R.; Venugopal, V. R.;
Spangler, S. R.; Kundu, M. R.; Evans, D. S.
Bibliographic Code: 1977ApJ...216..479K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1977ApJ...216..479K
@--------------------------------------------------------------------
Title: Observations of the quiet sun at meter and decameter
wavelengths
Authors: Kundu, M. R.; Erickson, W. C.; Gergely, T. E.
Bibliographic Code: 1977SoPh...53..489K
Abstract
The new TeePee Tee array of the Clark Lake Radio Observatory has been
used to observe the quiet sun at 121.5, 73.8 and 26.3 MHz. The
equatorial brightness distributions at all three frequencies, and the
polar brightness distributions at the two higher ones have been
measured. From the observed total fluxes and half-power diameters we
have derived the peak brightness temperatures of the solar disk as well
as of some sources of the slowly varying component.
@--------------------------------------------------------------------
Title: 3.5 MM depression features associated with H-alpha
'disparitions brusques'
Authors: Kundu, M. R.; Lantos, P.
Bibliographic Code: 1977SoPh...52..393K
Abstract
The characteristics of 3.5-mm depression features associated with two
'disparation brusques' observed in H-alpha are discussed. The millimeter
depressions still exist, although reduced in strength, after the
disappearance of the H-alpha filament. The two depressions correspond to
temperatures of 600 and 450 K before and to 200 and 250 K after the
disappearance of the H-alpha filament.
@--------------------------------------------------------------------
Title: 6 centimeter observations of solar active regions
with 6 SEC resolution
Authors: Kundu, M. R.; Alissandrakis, C. E.; Bregman, J. D.;
Hin, A. C.
Bibliographic Code: 1977ApJ...213..278K
Abstract
We have used the Westerbork Synthesis Radio Telescope for observations
of solar active regions at 6 cm during 1974 May 8-10. The particular
problems of using a sidereal instrument for solar observations are
discussed. Maps of total intensity and circular polarization were
obtained for four active regions with sunspots and a plage region; the
linear polarization was below the noise limit. The brightest components
of the 6 cm emission are associated with sunspots, while weaker
components are associated with the plage magnetic fields, both
longitudinal and transverse. An inversion of the sense of circular
polarization was observed in the preceding part of a region with bipolar
magnetic-field structure, about two days after the region passed through
the central meridian. Nine bursts were also observed, and their
one-dimensional positions with respect to the associated active regions
are given.
@--------------------------------------------------------------------
Title: Brightness distributions of the sun at 33 and 37 GHz
Authors: Kundu, M. R.; Liu, S.-Y.; McCullough, T. P.
Bibliographic Code: 1977SoPh...51..321K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1977SoPh...51..321K
@--------------------------------------------------------------------
Title: Polarization Properties of Solar Bursts at 6 cm
Wavelength.
Authors: Kundu, M. R.; Allisandrakis, C. E.
Bibliographic Code: 1977BAAS....9R.328K
Abstract
@--------------------------------------------------------------------
Title: Decameter Observations of the White Light Coronal
Transient of October 27, 1973
Authors: Gergely, T. E.; Kundu, M. R.; Erickson, W. C.
Bibliographic Code: 1977BAAS....9Q.369G
Abstract
@--------------------------------------------------------------------
Title: Determination of the Decameter Wavelength Spectrum
of the Quiet Sun.
Authors: Erickson, W. C.; Gergely, T. E.; Kundu, M. R.;
Mahoney, M. J.
Bibliographic Code: 1977BAAS....9..371E
Abstract
@--------------------------------------------------------------------
Title: A Study of Filament Transition Sheath from Radio
Observations.
Authors: Rao, A. P.; Kundu, M. R.
Bibliographic Code: 1977BAAS....9..314R
Abstract
@--------------------------------------------------------------------
Title: 5 GHz observations of galactic supernova remnants
Authors: Angerhofer, P. E.; Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1977A&A....55...11A
Abstract
Brightness and polarization distributions over several galactic
supernova remnants have been observed at a wavelength of 6 cm. These
observations have confirmed the nonthermal nature of most of the
observed sources. It is suggested, however, that the objects G33.1-0.1
(KES 78), G35.6-0.0, G37.6-0.1, G37.7+0.1, and G37.9-0.4 are thermal.
The results of these observations are presented in the form of total
intensity contour maps with superimposed polarization vectors.
@--------------------------------------------------------------------
Title: A comparison of positions and sizes of sources of
centimeter and X-ray bursts
Authors: Kundu, M. R.; Alissandrakis, C. E.; Kahler, S. W.
Bibliographic Code: 1976SoPh...50..429K
Abstract
Results are reported for a parallel study of three centimeter-wave radio
bursts observed on August 9, 1973, with the NRAO three-element
interferometer at 3.7 and 11.1 cm and the associated X-ray flares
observed with the S-054 telescope aboard Skylab. Within the errors of
the measurements, the radio and X-ray events are cospatial. Good
agreement is found between the size of the X-ray kernel and that of the
core of the centimeter burst, but there is evidence that much of the
impulsive radio flux was produced in a larger area.
@--------------------------------------------------------------------
Title: Observations of Solar Bursts at 6 cm Wavelength with
Angular Resolution of 6" arc.
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1976BAAS....8Q.555A
Abstract
@--------------------------------------------------------------------
Title: Observations of Jupiter's Radio Emission at 327 MHz
and 1410 MHz During the Pioneer 11 Fly
Authors: Kundu, M. R.; Sarma, N. V. G.; Gerard, E.
Bibliographic Code: 1976BAAS....8..504K
Abstract
@--------------------------------------------------------------------
Title: Observation of a coronal hole at 85 GHz
Authors: Kundu, M. R.; Liu, S.-Y.
Bibliographic Code: 1976SoPh...49..267K
Abstract
A coronal hole was observed at 85 GHz (3.5 mm) on Nov. 24, 1970, when a
spectacular coronal hole was observed in soft X-rays. The millimeter
counterpart of the hole is much weaker and less widespread than in
X-rays. The brightness temperature inside the hole was in most places
about 100 to 200 K lower than the mean brightness temperature of the sun
at 85 GHz.
@--------------------------------------------------------------------
Title: Observations of intensity and linear polarization of
CTB 80 at 6 and 2.8 CM
Authors: Velusamy, T.; Kundu, M. R.; Becker, R. H.
Bibliographic Code: 1976A&A....51...21V
Abstract
The paper presents observations of the distribution of intensity and
linear polarization over the radio source CTB 80 at 6 and 2.8 cm. The
physical nature of the source is examined, particularly the relation
between the strong central component and a ridgelike structure that
extends across the northern half in the E-W direction. The structure,
nonthermal spectrum, and polarization of the central component are found
to be very similar to those of a supernova remnant, but the ridge is
shown to be unlike any feature of any other SNR. It is suggested that
the ridge may have resulted from expansion of the remnant shell into a
dense interstellar cloud or, alternatively, that CTB 80 might be a
nearby extragalactic radio source similar to Centaurus A.
@--------------------------------------------------------------------
Title: 3.7 and 11.1 centimeter observations of the radio
galaxy 3C 386
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1976ApJ...207...29B
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1976ApJ...207...29B
@--------------------------------------------------------------------
Title: A decameter type II burst associated with a
behind-the-limb flare
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1976SoPh...48..357G
Abstract
The characteristics of a decametric type II burst associated with a
possible behind-the-limb flare are discussed. The burst source had an
unusually high velocity. Assuming that the disturbance propagated as an
MHD wave, the magnetic field strength at the 40-MHz plasma level is
estimated to be 5.6 gauss.
@--------------------------------------------------------------------
Title: High-resolution radio observations of three
supernova remnants
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1976ApJ...204..427B
Abstract
The paper presents and discusses radio observations of three supernova
remnants (G21.5-0.9, G29.7-0.3, and 3C 391) made at 3.7 and 11.1
centimeters. The supernova remnant G21.5-0.9 has an elliptical
brightness distribution and is similar to the Crab Nebula as well as 3C
58 in appearance and spectrum. The two remnants G29.7-0.3 and 3C 391
both show a broken shell structure typical of most galactic supernova
remnants.
@--------------------------------------------------------------------
Title: A search for radio halos around pulsars
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1976ApL....17..177V
Abstract
Observations of regions around 24 pulsars at 11, 21, and 40 cm are
presented. Very extended sources have been observed close to the nearby
pulsars 1642-03 and 1706-16. Double source structure with the pulsar on
the line of separation has been found around four pulsars. The proper
motions of pulsars 0823 + 26, 0834 + 06, 1133 + 16, and 2016 + 28 seem
to be consistent with their possible association with the nearby
continuum sources. The possibility that some of these sources may be
radio halos or ghost remnants associated with the pulsars is discussed.
@--------------------------------------------------------------------
Title: Differential rotation of the solar atmosphere as
determined from millimeter data
Authors: Liu, S.-Y.; Kundu, M. R.
Bibliographic Code: 1976SoPh...46...15L
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1976SoPh...46...15L
@--------------------------------------------------------------------
Title: Observations of Jupiter's radio emission at 327 MHz
and 1410 MHz during the Pioneer 11 fly-by
Authors: Kundu, M. R.; Sarma, N. V. G.; Gerard, E.
Bibliographic Code: 1976ApL....18...41K
Abstract
During the 1974 fly-by of Jupiter by the Pioneer 11 spacecraft, radio
observations were carried out daily at 327 and 1410 MHz for a period of
60 days centered on December 3, 1974, the day of closest approach to
Jupiter. The 1410-MHz data reveal two significant short-term variations
in the Jovian radio emission; the largest one is probably present also
at 327 MHz although Faraday rotation in earth's ionosphere could have
affected the data. The two radio bursts appear to be correlated with two
long-duration electron bursts observed in the energy ranges from 2 to 7
and 6 to 30 MeV.
@--------------------------------------------------------------------
Title: On the structure of filaments from centimeter and
millimeter observations
Authors: Butz, M.; Fuerst, E.; Hirth, W.; Kundu, M. R.
Bibliographic Code: 1975SoPh...45..125B
Abstract
From filament observations at centimeter and millimeter wavelengths, it
is shown that the transition layer between the dense cool filamentary
material and the ambient hot rarified corona is rather thin, of the
order of some hundred kilometers. Hence, the difference in the sizes of
filaments in the radio and optical domains is of the order of 1000 km or
2 sec, thus not detectable by the instruments so far used for
observations of filaments.
@--------------------------------------------------------------------
Title: Comments on the quiet sun brightness distribution at
1.2 MM wavelength
Authors: Kundu, M. R.; Liu, S.-Y.
Bibliographic Code: 1975SoPh...44..361K
Abstract
Data on the center-to-limb brightness distribution of the quiet sun at
1.2-mm wavelength are reanalyzed. The observed brightness distribution
at this wavelength is plotted along the equatorial direction and
analyzed to determine whether it is uniform, limb-brightened, or
limb-darkened. It is concluded that at the present time, there is no
evidence for a uniform or limb-brightened distribution at 1.2 mm from
either an observational or theoretical point of view.
@--------------------------------------------------------------------
Title: Observations at 6 CM of the solar active region
Authors: Kundu, M. R.; Alissandrakis, C. E.
Bibliographic Code: 1975Natur.257..465K
Abstract
Preliminary results are reported for the synthesis of a solar active
region from observations with a synthesis radio telescope at a
wavelength of 6 cm. Several individual sources are observed in the
total-intensity and circular-polarization maps. These are shown to
correspond to two large sunspots, two groups of small sunspots, and a
plage. A magnetogram indicates that this active region had a bipolar
structure with positive polarity concentrated on the main sunspots and
negative polarity scattered over the plage and some of the small
sunspots. It is noted that several radio bursts were recorded during the
observation period and that one corresponded to a H-alpha flare near one
of the sunspot groups.
@--------------------------------------------------------------------
Title: A search for periodic variations of solar radio
emission at 3.7- and 11.1-cm wavelengths
Authors: Kundu, M. R.; Alissandrakis, C. E.
Bibliographic Code: 1975MNRAS.173...65K
Abstract
Periodic time variations in the emission of quiet solar regions were
sought with the NRAO three-element interferometer at 3.7 and 11.1 cm.
The visibility function of a source as obtained with a tracking
interferometer is an implicit function of time, because of projected
baseline changes, and therefore only observations taken when the
baseline changes vary slowly with time were used. The visibility
function shows significant time variations, but a power-spectrum
analysis of the data revealed no unique periodicity.
@--------------------------------------------------------------------
Title: Observations of nine supernova remnants at 10.6 GHz
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1975AJ.....80..679B
Abstract
Intensity contour and polarization observation maps of nine supernova
remnants at a microwave frequency are presented and discussed. The data
provided are the highest-frequency (10.6 GHz) measurements to date for
several of these sources and should therefore be useful in determining
their spectra. Polarization ranges from 2 or 3% to as high as 40-50%.
Integrated fluxes for the sources vary from about 3 to more than 25.
@--------------------------------------------------------------------
Title: Depolarization of five supernova remnants - Internal
and external Faraday effects
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1975A&A....41..307V
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1975A&A....41..307V
@--------------------------------------------------------------------
Title: High Resolution Polarization Observations of a Solar
Active Region at 6 cm.
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1975BAAS....7..473A
Abstract
@--------------------------------------------------------------------
Title: Decameter storm radiation. II
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1975SoPh...41..163G
Abstract
The height, size, directivity, and lifetime of decametric storm sources
are investigated. The height of the continuum sources is determined from
the rotation rate, and the gradient of electron density for the regions
of storm origin is computed by assuming that the radiation originates at
the plasma frequency. The mean angular size of the sources is found to
be quite large (increasing with decreasing frequency), the storm
continuum is strongly directive toward the disk center, and east-west
asymmetry is observed at decameter wavelengths. Two distinct classes of
type III bursts are observed during storms: 'off-fringe' (displaced in
position from the continuum source) and 'on-fringe' (coinciding in
position with the continuum). A model of the storm region is proposed in
which the 'on-fringe' bursts originate in regions of diverging field
lines above closed magnetic loops and the 'off-fringe' bursts are
excited by energetic electron streams having access to open field lines
at the base of the loops.
@--------------------------------------------------------------------
Title: High resolution observations of solar bursts at 3.7
and 11.1 CM wavelengths
Authors: Alissandrakis, C. E.; Kundu, M. R.
Bibliographic Code: 1975SoPh...41..119A
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1975SoPh...41..119A
@--------------------------------------------------------------------
Title: A Possible Relation Between z-Distribution and
Spectral Index for Galactic Supernova Remnants.
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1975BAAS....7R.247B
Abstract
@--------------------------------------------------------------------
Title: 6 cm Observations of A Solar Active Region with the
Westerbork Synthesis Radio Telescope.
Authors: Kundu, M. R.; Alissandrakis, C. E.;
van Someren Greve, H. W.
Bibliographic Code: 1975BAAS....7..235K
Abstract
@--------------------------------------------------------------------
Title: Highly polarized radio outburst from Cygnus X-3.
Authors: Seaquist, E. R.; Gregory, P. C.; Perley, R. A.;
Becker, R. H.; Carlson, J. B.; Kundu, M. R.;
Bignell, R. C.; Dickel, J. R.
Bibliographic Code: 1975JRASC..69...42S
Abstract
@--------------------------------------------------------------------
Title: A possible relation between spectral index and
z-distribution for supernova remnants
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1975A&A....38..149B
Abstract
A statistical relation has been found between spectral index and the
mean distance from the galactic plane for supernova remnants. Using
z-distances calculated from the Sigma-D relationship and the observed
spectral indices at radio frequencies for 93 galactic supernova
remnants, the mean z-distance is found to vary from 175 pc to 60 pc for
remnants with flat and steep spectra, respectively. A possible
correlation between flat-spectra supernova remnants and pulsars is
discussed.
@--------------------------------------------------------------------
Title: Ghost remnants around pulsars.
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1975BASI....3R..35V
Abstract
@--------------------------------------------------------------------
Title: Highly polarised radio outburst from Cygnus X-3
Authors: Seaquist, E. R.; Gregory, P. C. ; Perley, R. A.;
Becker, R. H.; Carlson, J. B.; Kundu, M. R.;
Bignell, R. C.; Dickel, John R.
Bibliographic Code: 1974Natur.251..394S
Abstract
WE report here the results of extensive observations of a new series of
outbursts from Cyg X-3 which we commenced following the recent IAU
telegram alert from Sir Martin Ryle. A high degree of linear
polarisation has been discovered in one of the recent outbursts. The
degree of polarisation changes over a period of 17 d and reaches a
maximum of 14%. The observations indicate a high degree of order in the
source magnetic field and that a thermal plasma coexists with the
radiating relativistic electrons. In addition, a new upper limit of
0.05'' has been obtained for the angular size of Cyg X-3, together with
an improved position for the source.
@--------------------------------------------------------------------
Title: Polarization of supernova remnants: internal Faraday
effects and derived magnetic fields.
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1974BASI....2...38V
Abstract
@--------------------------------------------------------------------
Title: Absence of Periodic Variation in Solar Radiation at
3.7 cm and 11.1 cm Wavelengths.
Authors: Alissandrakis, C.; Kundu, M. R.; Becker, R. H.
Bibliographic Code: 1974BAAS....6..348A
Abstract
@--------------------------------------------------------------------
Title: High Resolution Observations of Five Possible
Supernova Remnants at Centimeter Wavelengths.
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1974BAAS....6..313B
Abstract
@--------------------------------------------------------------------
Title: Observations of intensity and linear polarization in
supernova remnants at 11 cm wavelength.
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1974A&A....32..375V
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1974A&A....32..375V
@--------------------------------------------------------------------
Title: Meter and decameter wavelength positions of solar
bursts of July 31 August 7, 1972
Authors: Kundu, M. R.; Erickson, W. C.
Bibliographic Code: 1974SoPh...36..179K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1974SoPh...36..179K
@--------------------------------------------------------------------
Title: Decameter Type IV Bursts Associated with Coronal
Transients
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1974SoPh...34..433G
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1974SoPh...34..433G
@--------------------------------------------------------------------
Title: Polarization of supernova remnants KE 69, G
357.7-0.1, HC 26, and gamma Cygni at 6- and 2.8-cm
wavelengths.
Authors: Kundu, M. R.; Velusamy, T.; Hardee, P. E.
Bibliographic Code: 1974AJ.....79..132K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1974AJ.....79..132K
@--------------------------------------------------------------------
Title: Fine Structure of a Solar Flare Region at 3.7 and
11.1 cm Wavelengths
Authors: Kundu, M. R.; Velusamy, T.; Becker, R. H.
Bibliographic Code: 1974SoPh...34..217K
Abstract
On June 9, 1973, a flare associated burst was observed with the NRAO
3-element interferometer at 3.7 and 11.1 cm wavelength. The burst was of
`gradual rise and fall' type. Comparing the fringe
amplitudes at 3.7 cm to the visibility computed for model flare regions
we found that the precursor data are best fitted by a region of 3"
in size while at the time of the peak, the flare appears to have a size
of 2". During the post-maximum phase a size of 5" is the
best estimate. Similar computations have been done for 11.1 cm data. The
peak brightness temperatures are 1.2 × 109 K and 1.65
× 108 K at 3.7 and 11.1 cm respectively. Such high
temperatures would imply that a significant fraction of the burst
radiation has a non-thermal origin.
@--------------------------------------------------------------------
Title: Fine Structure of a Solar Active Region at 3.7 and
11.1 cm Wavelengths
Authors: Kundu, M. R.; Becker, R. H.; Velusamy, T.
Bibliographic Code: 1974SoPh...34..185K
Abstract
@--------------------------------------------------------------------
Title: Fine Structure of the Sun at 1.3 cm Wavelength
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1974SoPh...34..125K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1974SoPh...34..125K
@--------------------------------------------------------------------
Title: Long Base Line Interferometry of the Sun at 3.7 and
11.1 cm Wavelengths.
Authors: Kundu, M. R.; Alissandrakis, C.; Becker, R. H.
Bibliographic Code: 1974BAAS....6..219K
Abstract
@--------------------------------------------------------------------
Title: Decameter Type IV Bursts Associated with Coronal
Transients.
Authors: Gergely, T. E.; Kundu, M. R.
Bibliographic Code: 1974BAAS....6..218G
Abstract
@--------------------------------------------------------------------
Title: Meter and Decameter Wavelength Positions of Solar
Radio Bursts of July 31-AUGUST 7, 1972 (presented by
W.C. Erickson)
Authors: Kundu, M. R.; Errickson, W. C.
Bibliographic Code: 1974IAUS...57..231K
Abstract
@--------------------------------------------------------------------
Title: Fine structure of the sun at centimeter wavelengths.
Authors: Kundu, M. R.; Velusamy, T.; Becker, R. H.
Bibliographic Code: 1974IAUS...56...65K
Abstract
@--------------------------------------------------------------------
Title: Long Base-Line Interferometry of the Sun at
Centimeter Wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1974cesra...4...21K
Abstract
@--------------------------------------------------------------------
Title: Polarization of Solar Active Regions at 3.5
Millimeter Wavelength
Authors: Kundu, M. R.; Gergely, T.
Bibliographic Code: 1973SoPh...31..461K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1973SoPh...31..461K
@--------------------------------------------------------------------
Title: Interferometric Measurements of the Compact Source
2048+31
Authors: Becker, R. H.; Kundu, M. R.
Bibliographic Code: 1973NPhS..244..138B
Abstract
@--------------------------------------------------------------------
Title: Solar Active Regions at 9 and 3.5 mm Wavelengths
under Disturbed Conditions
Authors: Kundu, M. R.; Liu, Sou-Yang
Bibliographic Code: 1973SoPh...29..409K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1973SoPh...29..409K
@--------------------------------------------------------------------
Title: Polarization of the supernova remnant HB21 at 11-cm
wavelength
Authors: Kundu, M. R.; Becker, R. H.; Velusarny, T.
Bibliographic Code: 1973AJ.....78..170K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1973AJ.....78..170K
@--------------------------------------------------------------------
Title: Observations of the HII region S101 in Cygnus
Authors: Velusamy, T.; Kundu, M. R.
Bibliographic Code: 1973AJ.....78...31V
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1973AJ.....78...31V
@--------------------------------------------------------------------
Title: Millimeter Wavelength Observations of Solar Active
Regions
Authors: Kundu, M. R.
Bibliographic Code: 1973NASSP.342..104K
Abstract
@--------------------------------------------------------------------
Title: Polarization Structure of a Solar Flare Region at
9.5 mm Wavelength
Authors: Kundu, M. R.; McCullough, T. P.
Bibliographic Code: 1972SoPh...27..182K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1972SoPh...27..182K
@--------------------------------------------------------------------
Title: The Quiet Sun Brightness Distributions at Millimeter
Wavelengths and Chro mospheric Inhomogeneities
Authors: Lantos, P.; Kundu, M. R.
Bibliographic Code: 1972A&A....21..119L
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1972A&A....21..119L
@--------------------------------------------------------------------
Title: Observations of the Cygnus Loop at 6-cm Wavelength
Authors: Kundu, M. R.; Becker, R. H.
Bibliographic Code: 1972AJ.....77..459K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1972AJ.....77..459K
@--------------------------------------------------------------------
Title: Brightness and polarization structure of four
supernova remnants 3C 58, IC 443, W28, and W44 at
2.8 centimeter wavelength.
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1972A&A....20..237K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1972A&A....20..237K
@--------------------------------------------------------------------
Title: Observations of Prominences at 3.5 Millimeter
Wavelength
Authors: Kundu, M. R.
Bibliographic Code: 1972SoPh...25..108K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1972SoPh...25..108K
@--------------------------------------------------------------------
Title: Polarization of Solar Active Regions at 9.5 mm
Wavelength
Authors: Kundu, M. R.; McCullough, T. P.
Bibliographic Code: 1972SoPh...24..133K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1972SoPh...24..133K
@--------------------------------------------------------------------
Title: Solar Radio Emission at 1.2 mm Wavelength
Authors: Kundu, M. R.
Bibliographic Code: 1971SoPh...21..130K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1971SoPh...21..130K
@--------------------------------------------------------------------
Title: CP 1919-No confirmation of association with
G55.7+3.4
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1971NPhS..234...54K
Abstract
@--------------------------------------------------------------------
Title: Polarization of Solar Active Regions at 9 millimeter
Wavelength
Authors: Kundu, M. R.; McCullough, T. P.
Bibliographic Code: 1971BAAS....3R.449K
Abstract
@--------------------------------------------------------------------
Title: Brightness and polarization structure of four
supernova remnants at 2.8 centimeter wavelength.
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1971BAAS....3..499K
Abstract
@--------------------------------------------------------------------
Title: Polarization of the Supernova Remnant HB 21 AT a
Wavelength of 6 Centi-Meters
Authors: Kundu, M. R.
Bibliographic Code: 1971ApJ...165L..55K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1971ApJ...165L..55K
@--------------------------------------------------------------------
Title: Polarization of 3C10, 3C58 and several other radio
sources at 2.8 Centimeter Wavelength
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1971BAAS....3...21K
Abstract
@--------------------------------------------------------------------
Title: Polarization of Tycho's Supernova Remnant at a
Wavelength of 2.8 Centimeters
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1971ApJ...163..231K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1971ApJ...163..231K
@--------------------------------------------------------------------
Title: Active Regions at Millimeter Wavelength and the
Measurement of Magnetic Fields
Authors: Kundu, M. R.
Bibliographic Code: 1971IAUS...43..642K
Abstract
@--------------------------------------------------------------------
Title: Solar Bursts at Decameter and Hectometer Wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1971ASSL...27..287K
Abstract
@--------------------------------------------------------------------
Title: Positions and Motions of Solar Bursts at Decameter
Wavelengths
Authors: Kundu, M. R.; Erickson, W. C.; Jackson, P. D.;
Fainberg, J.
Bibliographic Code: 1970SoPh...14..394K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1970SoPh...14..394K
@--------------------------------------------------------------------
Title: Brightness and Polarization Structure of Three
Supernova Remnants at 6-AND 11-CENTIMETER
Wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1970ApJ...162...17K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1970ApJ...162...17K
@--------------------------------------------------------------------
Title: Solar Active Regions at Millimeter Wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1970SoPh...13..348K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1970SoPh...13..348K
@--------------------------------------------------------------------
Title: The Slowly Varying Component of the Sun's Radiation
at Millimeter Wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1970BAAS....2T.203K
Abstract
@--------------------------------------------------------------------
Title: Polarization of the Cygnus Loop at 11-CENTIMETER
Wavelength
Authors: Kundu, M. R.
Bibliographic Code: 1969ApJ...158L.103K
Abstract
@--------------------------------------------------------------------
Title: Polarized Brightness Distributions of Supernova
Remnants IC 443 W44, and the Cygnus Loop at 6- and
11-cm Wavelengths
Authors: Kundu, M. R.
Bibliographic Code: 1969BAAS....1R.197K
Abstract
@--------------------------------------------------------------------
Title: Polarized Brightness Distributions of Supernova
Remnants IC 443 and W44 at 6-CM Wavelength
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1969ApJ...155..807K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1969ApJ...155..807K
@--------------------------------------------------------------------
Title: Possible Interpretation of Pulses from a Radio
Source
Authors: Kundu, M. R.; Chitre, S. M.
Bibliographic Code: 1968Natur.218.1037K
Abstract
THE Cambridge group1 recently announced the recording of
pulses from a local object, lasting for about 0.016 s and repeating with
extreme regularity with a period of 1.337 s, the accuracy being one part
in 107. There have been further observations from
Cambridge2 and from Jodrell Bank3. The amplitude
of the pulses varies randomly, the pulses appearing and disappearing for
periods of a few minutes. There is also a fine structure superimposed on
the main pulse. Despite the regularity of the pulses, the power emitted
varies significantly over all periods. Furthermore, observations
indicate a frequency drift of -5 MHz s-1. The absence of any
proper motion of the source, and the interpretation of the frequency
drift in terms of dispersion through the interstellar plasma, limit the
distance of the source to the range 103 A.U. 8 cm.
@--------------------------------------------------------------------
Title: Lunar Occupation of a Solar Active Region at 4 cm
Wavelength
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1968Natur.217.1132K
Abstract
THE solar eclipse of July 20, 1963, was observed from Ann Arbor,
Michigan, using the 85 ft. paraboloid telescope of the University of
Michigan. As observed from Michigan the solar eclipse was partial;
however, the Moon completely occulted two discrete regions on the
Sun-one near the east limb and the other near the west limb. We observed
the lunar occultation of the eastern region. At the 4 cm wavelength at
which this occultation was observed, the pencil beam of the radio
telescope had a half-power width of 5'.95 of arc. Drift scans were taken
across the region before the occultation in order to find the position
of the peak. These scans indicated an angular size of about 3' of arc
and a position which was in agreement with the position indicated by
Stanford lambda 9.1 cm maps. Thus the beam almost completely covered
the discrete region, and the observations consisted in tracking the
region throughout the period of occultation with the beam pointed on the
peak of the region. The occultation was observed in both immersion and
emersion.
@--------------------------------------------------------------------
Title: Radio spectra of the nebula IC443
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1968MNRAS.140..173K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1968MNRAS.140..173K
@--------------------------------------------------------------------
Title: Some Properties of the Sources of Slowly Varying
Component and of Bursts at 612 MC S
Authors: Swarup, G.; Kundu, M. R.; Kapahi, V. K.;
Isloor, J. D.
Bibliographic Code: 1968IAUS...35..581S
Abstract
@--------------------------------------------------------------------
Title: A study of the Cygnus loop at 430, 195 and 41 MHz
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1967AnAp...30..723K
Abstract
@--------------------------------------------------------------------
Title: A study of galactic sources W 51 and W 44
Authors: Kundu, M. R.; Velusamy, T.
Bibliographic Code: 1967AnAp...30...59K
Abstract
@--------------------------------------------------------------------
Title: Buchbesprechungen über: Solar Radio Astronomy. (Ref.
A. UNSÖLD)
Authors: Kundu, M. R.
Bibliographic Code: 1967ZA.....66..339K
Abstract
@--------------------------------------------------------------------
Title: Lunar Occultation of the Radio Sources 0938 + 18 and
1101 + 11
Authors: Cohen, M. H.; Kundu, M. R.
Bibliographic Code: 1966ApJ...143..621C
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1966ApJ...143..621C
@--------------------------------------------------------------------
Title: Occultation of Taurus-A by the Solar Corona at 430
Mc/s in June 1964
Authors: Kundu, M. R.
Bibliographic Code: 1965Natur.205..683K
Abstract
DURING June of every year, the radio source Taurus-A passes within a
small angular distance of the Sun. This particular situation, commonly
referred to as the occultation of Taurus-A by the Sun, permits an
investigation of the Sun's outer corona as the radio source is viewed
through it. The measurements made over the past several years have
demonstrated that the radiation from the source is scattered at the
electron density irregularities in the corona; as a result one observes
an apparent broadening of the source accompanied by a decrease of its
intensity. The effect becomes larger with decreasing angular separation
of the source from the Sun. This phenomenon has been observed in the
range of frequencies 26-178 Mc/s1-5. At wave-lengths of 6 and
18 cm the effect has been reported to be negative6,7, except
that a positive result has been reported on 10- and 25-cm
wave-lengths8. The results on all metre and decametre
wave-lengths are consistent and are in accordance with the theory of
small-angle multiple scattering, in which the angular size of the
scattered distribution is proportional to the square of the wave-length.
However, the increase of intensity on 169 Mc/s at 7 R0
(R0 is the photospheric radius) from the centre of the Sun is
not consistent with the theoretical prediction based on the lower
frequency data5. In order to investigate if the coronal
scattering is still effective at frequencies higher than 169 Mc/s, and
in particular to see if the increase of intensity is also observed on
430 Mc/s, we undertook to observe at 430 Mc/s the occultation of
Taurus-A by the solar corona in June 1964, using the 1,000-ft. dish of
the Arecibo Ionospheric Observatory.
@--------------------------------------------------------------------
Title: Some Aspects of the Type-IV Continuum Radiation on
Decimeter Wave-lengths
Authors: Kundu, M. R.
Bibliographic Code: 1965ASSL....1..408K
Abstract
@--------------------------------------------------------------------
Title: A Survey of the Interpretations of Radio and X-Ray
Bursts
Authors: Kundu, M. R.
Bibliographic Code: 1964NASSP..50..335K
Abstract
@--------------------------------------------------------------------
Title: Centimeter-Wave Radio and X-Ray Emission from the
Sun
Authors: Kundu, M. R.
Bibliographic Code: 1963SSRv....2..438K
Abstract
@--------------------------------------------------------------------
Title: Spectral Characteristics of Solar Continuum
Radiation in the 500-1000 Mc/s Range.
Authors: Kundu, M. R.; Spencer, C. L.
Bibliographic Code: 1963ApJ...137..572K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1963ApJ...137..572K
@--------------------------------------------------------------------
Title: Association of Centimeter-Wave Bursts with Different
Spectral Types of Meter-Wave Burst of Solar Radio
Emission
Authors: Kundu, M. R.
Bibliographic Code: 1962JGR....67.2695K
Abstract
@--------------------------------------------------------------------
Title: Some Relations between Centimeter-Wave Radio Bursts
and Solar Cosmic Rays and X-Rays
Authors: Kundu, M. R.
Bibliographic Code: 1962JPSJS..17B.259K
Abstract
@--------------------------------------------------------------------
Title: The Nature of Type IV Solar Radio Bursts
Authors: Kundu, M. R.
Bibliographic Code: 1962JPSJS..17B.215K
Abstract
@--------------------------------------------------------------------
Title: Bursts of Centimeter-Wave Emission and the Region of
Origin of X Rays from Solar Flares
Authors: Kundu, M. R.
Bibliographic Code: 1961JGR....66.4308K
Abstract
@--------------------------------------------------------------------
Title: Interferometric Studies of Type IV Solar Bursts of
Continuum Radiation on 340 and 87 Mc/s.
Authors: Kundu, M. R.; Firor, J. W.
Bibliographic Code: 1961ApJ...134..389K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1961ApJ...134..389K
@--------------------------------------------------------------------
Title: Some Studies on the Occurrence of Type IV Solar
Bursts of Continuum Radiation.
Authors: Kundu, M. R.
Bibliographic Code: 1961AJ.....66..289K
Abstract
@--------------------------------------------------------------------
Title: Some Studies on the Occurrence of Type IV Solar
Bursts of Continuum Radiation.
Authors: Kundu, M. R.
Bibliographic Code: 1961ApJ...134...96K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1961ApJ...134...96K
@--------------------------------------------------------------------
Title: A Comparison of the Dynamic Spectra of Solar Radio
Bursts in the Decimeterand Meter-Wave Ranges.
Authors: Kundu, M. R.; Roberts, J. A.; Spencer, C. L.;
Kuiper, J. W.
Bibliographic Code: 1961ApJ...133..255K
Abstract
Abstract image available at:
http://esoads.eso.org/abs/1961ApJ...133..255K
@--------------------------------------------------------------------
Title: Solar Radio Emission on Centimeter Waves and
Ionization of the E Layer of the Ionosphere
Authors: Kundu, M. R.
Bibliographic Code: 1960JGR....65.3903K
Abstract
@--------------------------------------------------------------------
Title: A Relation Between Solar Radio Emission and Polar
Cap Absorption of Cosmic Noise
Authors: Kundu, M. R.; Haddock, F. T.
Bibliographic Code: 1960Natur.186..610K
Abstract
@--------------------------------------------------------------------
Title: Time Relationship of Metre-Wave and 3-cm. Wave
Bursts
Authors: Kundu, M. R.
Bibliographic Code: 1959Natur.183.1047K
Abstract
IT is known that solar bursts are observed over a very large range of
wave-lengths. A single burst may extend over a large or small fraction
of the range from centimetres to metres. Usually, bursts of strong
intensity in the centimetre region are associated with great bursts
observed on metre waves. It is generally believed that at the time of
these bursts, radial ascension of ionized particles excites
radio-frequency radiation at different levels in the solar atmosphere.
Moreover, there are reasons for thinking that solar radio waves on the
lower frequencies are emitted at a higher altitude in the solar
atmosphere than those on the higher frequencies. As a result we observe
a regular drift of the onset of the bursts towards the lower
frequencies. The object of this communication is to discuss a relation
existing between the times of commencement of the bursts observed on
3-cm. waves and on metre waves. This work is based chiefly upon
measurements of the associated 3-cm. wave bursts made by means of an int
erferometer1.
@--------------------------------------------------------------------
Title: Structures et propriétés des sources
d'activité solaire sur ondes centimétriques
Authors: Kundu, M. R.
Bibliographic Code: 1959AnAp...22....1K
Abstract
@--------------------------------------------------------------------
Title: Etude interférométrique des sources d'activité
solaire sur 3 CM de longueur d'onde
Authors: Kundu, M. R.
Bibliographic Code: 1959IAUS....9..222K
Abstract
@--------------------------------------------------------------------
Title: Thunderstorms and Sporadic E Ionization of the
Ionosphere
Authors: Mitra, S. K.; Kundu, M. R.
Bibliographic Code: 1954Natur.174..798M
Abstract
IN the course of the ionospheric observations carried out at Calcutta
(lat. 22° 33' N., long. 88° 21' E.) for more than two decades,
it had always been found that sporadic E ionization (Es) is
greatly increased during the occurrence of thunderstorms. In view of the
persistence of the phenomenon, it was thought worth while to make a
close.study of the increase of Es ionization during the
occurrence of severe thunderstorms of the squall type, known as
`nor'westers', which are a special feature of the weather of this part
of India (Bengal) in the pre-monsoon months March-May. During these
thunderstorms the wind generally blows from a north-westerly direction
with velocity often exceeding 50 miles/hr. The thunderstorms are
invariably accompanied by lightning discharges.