scholarly journals High-Resolution Dynamic Spectrum of a Spectacular Radio Burst from AD Leonis

1995 ◽  
Vol 151 ◽  
pp. 32-35
Author(s):  
Meil Abada-Simon ◽  
Alain Lecacheux ◽  
Monique Aubier ◽  
Jay A. Bookbinder
Keyword(s):  
High Resolution ◽  
Dynamic Spectrum ◽  
Plasma Radiation ◽  
The Sun ◽  
Radio Bursts ◽  
Radio Radiation ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Cyclotron Maser ◽  
Intense Burst

AD Leonis is a very active, single dMe flare star. The similarities between this type of star and the Sun has led to study their radio radiation, which originates from their corona. The high brightness temperatures and other characteristics of most dMe radio bursts can be attributed to a non-thermal, coherent mechanism: plasma radiation or a cyclotron maser instability (CMI) are both plausible explanations. Even for the strongest burst of AD Leo which reached 940 mJy at 21 cm, it was not possible to discriminate between these two mechanisms (Bastian et al. 1990).Here we present an intense burst from AD Leo, exhibiting strong spikes for which the CMI seems to be the only reasonable explanation. In Sect. 2 we describe the observations, and in Sect. 3 we give an interpretation for this event.

scholarly journals Solar Decimetre Radio Bursts

1963 ◽  
Vol 16 (1) ◽  
pp. 8 ◽  
Author(s):  
RF Mullaly ◽  
T Krishnan
Keyword(s):  
High Resolution ◽  
Burst Activity ◽  
Radio Interferometer ◽  
The Sun ◽  
Radio Bursts ◽  
Solar Burst ◽  
Brightness Temperatures ◽  
Plage Region ◽  
East West ◽  
Eastern Half

High resolution studies (2' of arc beam) were made with the east�west arm of the Christiansen radio interferometer for about 50 21�cm solar burst events during 1958-1961. The burst sources were always closely associated in position with already existing radio plage regions of the Sun's slowly varying decimetre radiation. They had sizes of from 2 to 5' of arc, never exceeded but often approached in size their parent plage region, and showed no major movements during their development. Brightness temperatures ranged up to 2 X 109 OK (mostly between 107 and 108 OK). More bursts were observed near the Sun's centre than near the limb, and more on the western than on the eastern half. There was also a curious "gap" of 30� longitude on the eastern half of the Sun with virtually no burst activity.

Observations of High Brightness Temperatures in Moving Type IV Solar Radio Bursts

1978 ◽  
Vol 3 (4) ◽  
pp. 247-249 ◽  
Author(s):  
R. T. Stewart ◽  
R. A. Duncan ◽  
S. Suzuki ◽  
G. J. Nelson
Keyword(s):  
Synchrotron Radiation ◽  
Second Phase ◽  
Synchrotron Emission ◽  
Radio Bursts ◽  
Solar Radio Bursts ◽  
High Brightness ◽  
Fast Electrons ◽  
Circularly Polarized ◽  
Brightness Temperatures ◽  
Type Iv

It has generally been accepted that moving type IV bursts are generated as synchrotron radiation from energetic electrons high in the solar corona (Boischot and Denisse 1957). At 80 MHz the peak brightness temperature is usually ~ 108 K and the radiation becomes highly circularly polarized as the burst decays. This has led several authors (Kai 1969; Dulk 1970, 1973; Schmahl 1972; Robinson 1974, 1977; Nelson 1977) to the conclusion that the radiation comes from mildly relativistic (~ 100 keV) electrons and occurs at low harmonics of the gyro-frequency (gyro-synchrotron radiation). We present evidence of moving type IV bursts at 43, 80 and 160 MHz with brightness temperatures of ~ 109 K, and one at 43 MHz as high as 1010 K. The number (~ 1033) of energetic (≥ 1 MeV) electrons which is required in order to explain such high brightness temperatures by incoherent gyro-synchrotron emission is very large and near the upper limit for the number of fast electrons accelerated in the second phase of a solar flare. If amplification takes place a smaller number of electrons with energies ~ 100 keV would be required.

scholarly journals An Interpretation of Solar Flare Microwave Spikes as Gyrosynchrotron Masering

1980 ◽  
Vol 86 ◽  
pp. 457-459 ◽  
Author(s):  
G. D. Holman ◽  
D. Eichler ◽  
M. R. Kundu
Keyword(s):  
Solar Flare ◽  
Solar Flares ◽  
Plasma Frequency ◽  
Microwave Emission ◽  
Plasma Radiation ◽  
Alternative Possibility ◽  
High Brightness ◽  
Brightness Temperatures

Repeated bursts of microwave emission were observed by Slottje (1978) during the solar flares of April 11 and April 28, 1978. The high brightness temperatures which are inferred for these bursts indicate that a coherent mechanism must be responsible for the observed radiation. Slottje suggests that the emission is plasma radiation at the fundamental plasma frequency. We consider here the alternative possibility that the emission is coherent gyrosynchrotron radiation.

scholarly journals Flare stars at radio wavelengths

1990 ◽  
Vol 137 ◽  
pp. 125-138
Author(s):  
Kenneth R. Lang
Keyword(s):  
Active Regions ◽  
Plasma Radiation ◽  
Radio Radiation ◽  
Very Large Array ◽  
Brightness Temperatures ◽  
Stellar Flares ◽  
Long Duration ◽  
Electron Cyclotron Masers ◽  
Flare Stars ◽  
Radiation Processes

The radio emission from dMe flare stars is discussed using Very Large Array and Arecibo observations as examples. Active flare stars emit weak, unpolarized, quiescent radio radiation that may be always present. Although thermal bremsstrahlung and/or thermal gyroresonance radiation account for the slowly-varying, quiescent radio radiation of solar active regions, these processes cannot account for the long-wavelength quiescent radiation observed from nearby dMe flare stars. It has been attributed to nonthermal gyrosynchrotron radiation, but some as yet unexplained mechanism must be continually producing the energetic electrons. Long-duration (hours), narrow-band (Δv/v < 0.1) radiation is also emitted from some nearby dMe stars at 20 cm wavelength. Such radiation may be attributed to coherent plasma radiation or to coherent electron-cyclotron masers. Impulsive stellar flares exhibit rapid variations (< 100 msec) that require radio sources that are smaller than the star in size, and high brightness temperatures TB > 1015 K that are also explained by coherent radiation processes. Quasi-periodic temporal fluctuations suggest pulsations during some radio flares. Evidence for frequency structure and positive or negative frequency drifts during radio flares from dMe stars is also presented.

scholarly journals Fast radio bursts — A brief review: Some questions, fewer answers

2016 ◽  
Vol 31 (14) ◽  
pp. 1630013 ◽  
Author(s):  
J. I. Katz
Keyword(s):  
Column Density ◽  
Radio Bursts ◽  
Radio Radiation ◽  
Radio Pulsars ◽  
Soft Gamma Repeaters ◽  
Brightness Temperatures ◽  
Astronomical Object ◽  
Coherent Emission ◽  
Low Density Plasma ◽  
High Column

Fast radio bursts (FRBs) are millisecond bursts of radio radiation at frequencies of about 1 GHz, recently discovered in pulsar surveys. They have not yet been definitively identified with any other astronomical object or phenomenon. The bursts are strongly dispersed, indicating passage through a high column density of low density plasma. The most economical interpretation is that this is the intergalactic medium, indicating that FRB are at “cosmological” distances with redshifts in the range 0.3–1.3. Their inferred brightness temperatures are as high as 10[Formula: see text] K, implying coherent emission by “bunched” charges, as in radio pulsars. I review the astronomical sites, objects and emission processes that have been proposed as the origin of FRB, with particular attention to soft gamma repeaters (SGRs) and giant pulsar pulses.

Correlations of solar-flare electron events with radio and X-ray emission from the sun

1968 ◽  
Vol 46 (10) ◽  
pp. S757-S760 ◽  
Author(s):  
R. P. Lin
Keyword(s):  
Solar Flare ◽  
Solar Radio ◽  
Interplanetary Space ◽  
The Sun ◽  
Radio Bursts ◽  
Radio Observations ◽  
X Ray ◽  
Type Iii ◽  
Electron Event ◽  
Burst Emission

The > 40-keV solar-flare electrons observed by the IMP III and Mariner IV satellites are shown to be closely correlated with solar radio and X-ray burst emission. In particular, intense type III radio bursts are observed to accompany solar electron-event flares. The energies of the electrons, the total number of electrons, and the size of the electron source at the sun can be inferred from radio observations. The characteristics of the electrons observed in interplanetary space are consistent with these radio observations. Therefore these electrons are identified as the exciting agents of the type III emission. It has been noted that the radio and X-ray bursts are part of the flash phase of flares. The observations indicate that a striking feature of the flash phase is the production of electrons of 10–100 keV energies.

Observation of the Radio Radiation Flux of the Sun and Flares at a Wavelength of 5 cm

2020 ◽  
Vol 60 (8) ◽  
pp. 1087-1092
Author(s):  
A. G. Tlatov ◽  
V. M. Bogod ◽  
O. Pons ◽  
M. Rodriges ◽  
R. Estrada ◽  
...  
Keyword(s):  
Radiation Flux ◽  
The Sun ◽  
Radio Radiation

scholarly journals Hydrodynamic Models of Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 289-298
Author(s):  
Giovanni Peres
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Solar Flares ◽  
Impulsive Phase ◽  
Light Curves ◽  
Physical Parameters ◽  
The Sun ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

scholarly journals Quasi-Band-Limited Coronagraph for Extended Sources

2021 ◽  
Vol 10 (01) ◽  
pp. 2150002
Author(s):  
Igor Loutsenko ◽  
Oksana Yermolayeva
Keyword(s):  
High Resolution ◽  
High Ratio ◽  
Gravitational Lens ◽  
High Resolution Imaging ◽  
The Sun ◽  
Extended Source ◽  
Amplitude Image ◽  
Extended Sources ◽  
Resolution Imaging ◽  
Band Limited

We propose a class of graded coronagraphic “amplitude” image masks for a high throughput Lyot-type coronagraph that transmits light from an annular region around an extended source and suppresses light, with extremely high ratio, from elsewhere. The interior radius of the region is comparable with its exterior radius. The masks are designed using an idea inspired by approach due M. J. Kuchner and W. A. Traub (“band-limited” masks) and approach to optimal apodization by D. Slepian. One potential application of our masks is direct high-resolution imaging of exo-planets with the help of the Solar Gravitational Lens, where apparent radius of the “Einstein ring” image of a planet is of the order of an arc-second and is comparable with the apparent radius of the sun and solar corona.

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