A Gyro-Synchrotron Maser in the Solar Corona?

1978 ◽  
Vol 3 (3) ◽  
pp. 231-233 ◽  
Author(s):  
D. B. Melrose ◽  
S. M. White
Keyword(s):  
Synchrotron Radiation ◽  
Solar Corona ◽  
Brightness Temperature ◽  
Early Phase ◽  
Relativistic Electrons ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Type Iv ◽  
Alternative Suggestion ◽  
Lower Frequencies

Stewart (1978) has reported four moving type IV bursts observed with the Culgoora radio heliograph at 43, 80 and 160 MHz. After an early phase, the brightness temperatures of the observed bursts decreased with increasing frequency and with time. The highest brightness temperature observed at 43 MHz was 1010K, and it seems that the brightness temperature would have been still higher at even lower frequencies. Existing theoretical ideas on moving type IV bursts are based on data (at 80 MHz primarily) which included no brightness temperatures in excess of 109K. the accepted interpretation involved gyro-synchrotron radiation from mildly relativistic electrons (energies ≈ 100 keV); reabsorption by the electrons themselves restricts the brightness temperature to less than about 100 keV ≈ 109K (Wild and Smerd 1972, Dulk 1973). Stewart’s (1978) new data at 43 MHz require that this accepted interpretation be modified; he has suggested that higher energy electrons are involved. An alternative suggestion is explored here, namely that the absorption might be negative. In other words, the high brightness temperatures observed could be due to a gyro-synchrotron maser involving electrons with energies of about 100 keV.

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.

Outstanding Stellar Microwave Flares in 1986

1987 ◽  
Vol 7 (1) ◽  
pp. 55-59 ◽  
Author(s):  
O. B. Slee ◽  
G. J. Nelson ◽  
R. T. Stewart ◽  
Alan E. Wright ◽  
David L. Jauncey ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Main Sequence ◽  
Relativistic Electrons ◽  
Spectral Indices ◽  
Frequency Range ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Simultaneous Measurements ◽  
Gyrosynchrotron Emission ◽  
Large Frequency

AbstractWe describe bright microwave events that were first detected with the Parkes 64-m telescope at 8.4 or 22 GHz from six active-chromosphere stars. In some flares spectral data were obtained over a large frequency range from simultaneous measurements with the Parkes reflector (8.4 or 22 GHz), the Tidbinbilla interferometer (8.4 and 2.29 GHz), the Fleurs synthesis telescope (1.42 GHz) and the Molonglo Observatory synthesis telescope (0.843 GHz). Data on circular polarization were obtained from the Parkes observations at 8.4 GHz.The stars were in a wide variety of evolutionary states, ranging from a single pre-main-sequence star (HD 36705), two RS CVn binaries (HD 127535, HD 128171), an Algol (HD 132742) and two apparently single K giants (HD 32918 and HD 196818). Their high brightness temperatures, positive spectral indices and low polarization are consistent with optically thick gyrosynchrotron emission from mildly relativistic electrons with average energies 0.5 to 3 MeV gyrating in inhomogeneous magnetic fields of 5 to 100 G.

On the Polarization and Rapid Fade-out of Moving Type IV Solar Bursts

1970 ◽  
Vol 1 (8) ◽  
pp. 372-374 ◽  
Author(s):  
G. A. Dulk
Keyword(s):  
Synchrotron Radiation ◽  
Circular Polarization ◽  
Source Region ◽  
Relativistic Electrons ◽  
Constant Intensity ◽  
Precise Position ◽  
Polarization Measurements ◽  
Type Iv ◽  
Solar Bursts

Since the advent of the 80 MHz radioheliograph, precise position and polarization measurements have become available on several moving type IV bursts. Two of the more puzzling characteristics of these bursts are : (1) they exhibit strong circular polarization in parts or all of the source region ; (2) after moving outward to as much as 3 R⊙ with relatively constant intensity, they rapidly fade away. In this paper we discuss the polarization and intensity of synchrotron radiation from mildly relativistic electrons and suggest betatron deceleration as a mechanism to explain the rapid fade-out of the moving type IV sources. The results are applied to two examples of moving type IV bursts.

Observation of Strong Circular Polarization in a Moving Type IV Burst

1969 ◽  
Vol 1 (5) ◽  
pp. 189-191 ◽  
Author(s):  
K. Kai
Keyword(s):  
Synchrotron Radiation ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Circular Polarization ◽  
Type Iv ◽  
Weak Magnetic Fields

Since they were first interpreted, moving type IV bursts have been attributed to synchrotron radiation from electrons with energy ∼3 MeV radiating in weak magnetic fields (∼1 G) high in the solar corona. In this paper a description is given of 80 MHz radioheliograph observations of an outburst in which it was possible to isolate the moving type IV source and demonstrate that its circular polarization was strong (∼80%). Hence it is shown that the energy of the radiating electrons cannot exceed 6 = 105eV.

scholarly journals An Update on Radio Supernovae

1998 ◽  
Vol 164 ◽  
pp. 357-358 ◽  
Author(s):  
Schuyler D. Van Dyk ◽  
Richard A. Sramek ◽  
Kurt W. Weiler ◽  
Marcos J. Montes ◽  
Nino Panagia
Keyword(s):  
Synchrotron Radiation ◽  
Radio Emission ◽  
Brightness Temperature ◽  
Power Law ◽  
Progress Report ◽  
Light Curves ◽  
High Brightness ◽  
Turn On ◽  
Distance Indicators ◽  
Circumstellar Environment

AbstractThe radio emission from supernovae (SNe) is nonthermal synchrotron radiation of high brightness temperature, with a “turn-on” delay at longer wavelengths, power-law decline after maximum with index β, and spectral index α asymptotically decreasing with time to a final, optically thin value. Radio supernovae (RSNe) are best described by the Chevalier (1982) “mini-shell” model, with modifications by Weiler et al. (1990). RSNe observations provide a valuable probe of the SN circumstellar environment and constraints on progenitor masses. We present a progress report on a number of recent RSNe, as well as on new behavior from RSNe 1979C and 1980K, and on RSNe as potential distance indicators. In particular, we present updated radio light curves for SN 1993J in M81.

scholarly journals Summary

1974 ◽  
Vol 3 ◽  
pp. 493-498
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Radio Emission ◽  
Rotation Axis ◽  
Radiation Belts ◽  
Main Magnetic Field ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Pulsar Radiation ◽  
Wide Range

Professor G. R. A. Ellis reviewed the wide range of radio emission from Jupiter. At centimetric wavelengths the thermal radiation corresponds to a blackbody at 130K. Between 2 m and 10 cm wavelength there is a powerful component of synchrotron radiation from the electrons trapped in the radiation belts. At longer wavelengths there is a great variety of impulsive radio emission from coherent plasma oscillations.The magnetic field of Jupiter is known from the polarisation of the synchrotron radiation to be situated centrally (within one tenth of the radius) and inclined at 10° to the rotation axis. The radiating electrons have energies of the order of 10 MeV, and a density of 10”-3 cm-3, much greater than in the case of the Earth’s radiation belts.The decametric radiation varies with the rotation of Jupiter, possibly analogously to pulsar radiation. Bursts at around 4 MHz reach very high brightness temperatures, exceeding 1017 K. The occurrence of these strong bursts is closely related to the position of the Jovian satellite Io, which must have an interaction with the main magnetic field.

scholarly journals Intraday Variability and Microarcsecond Structure in Blazar Cores

2001 ◽  
Vol 205 ◽  
pp. 84-87 ◽  
Author(s):  
David L. Jauncey ◽  
Lucyna Kedziora-Chudczer ◽  
J. E. J. Lovell ◽  
Jean-Pierre Macquart ◽  
George D. Nicolson ◽  
...  
Keyword(s):  
William Shakespeare ◽  
Brightness Temperature ◽  
Circular Polarization ◽  
Julius Caesar ◽  
Principal Mechanism ◽  
High Brightness ◽  
Brightness Temperatures ◽  
Interstellar Scintillation ◽  
Intraday Variability

The accumulation of evidence now strongly favours interstellar scintillation (ISS) as the principal mechanism causing intra-day variability (IDV) at cm wavelengths. While ISS reduces the implied brightness temperatures, they remain uncomfortably high. The distance to the scattering screen is an important parameter in determining the actual brightness temperature encountered. The high brightness temperatures, the presence of strong and variable circular polarization and the observed lifetimes of a decade or more for several IDV sources, pose significant problems for synchrotron theory. “The fault, dear Brutus, is not in our stars, but in ourselves, that we are underlings.” William Shakespeare, Julius Caesar

scholarly journals Recent Very Bright Type IV Solar Metre-Wave Radio Emissions

1980 ◽  
Vol 91 ◽  
pp. 381-385 ◽  
Author(s):  
R. A. Duncan ◽  
R. T. Stewart ◽  
G. J. Nelson
Keyword(s):  
Radio Emission ◽  
Brightness Temperature ◽  
Radio Sources ◽  
Radio Emissions ◽  
Brightness Temperatures ◽  
Type Iv ◽  
Wave Radio

Stewart et al. (1978) have reported moving Type IV solar metre-wave radio outbursts with brightness temperatures between 108 and 1010 K. We now report Culgoora radioheliograph observations of four more Type IV radio sources, some moving, some stationary, but all with brightness temperatures above 109 K, and one with a brightness temperature above 1013 K. We also describe one of the previously reported events (that of 1977 September 20) in more detail. The interest of these events is that their high brightnesses place great strain upon the gyro-synchrotron theory of radio emission.

scholarly journals 80 MHz Radioheliograph Evidence on Moving Type IV Bursts and Coronal Magnetic Fields

1971 ◽  
Vol 43 ◽  
pp. 616-641 ◽  
Author(s):  
S. F. Smerd ◽  
G. A. Dulk
Keyword(s):  
Magnetic Field ◽  
Synchrotron Radiation ◽  
Magnetic Fields ◽  
Magnetized Plasma ◽  
Relativistic Electrons ◽  
Radiation Mechanism ◽  
Type Iv ◽  
Coronal Magnetic Fields ◽  
Field Lines ◽  
Magnetic Arch

The characteristics of 12 moving type IV bursts observed with the 80 MHz radioheliograph at the Culgoora Observatory between February 1968 and April 1970 are summarized.Three classes of moving sources can be recognized; they are described as: (1) Expanding arch; (2) Advancing front; (3) Isolated source.The first class has been identified (Wild, 1969) with the expansion of a magnetic arch or loop; the second class is here identified with an advancing MHD disturbance which may accelerate the radiating electrons in situ when moving at greater than Alfvén speed; the third with solar ejecta in the form of magnetized plasma clouds, or plasmoids. In all cases the radiation mechanism is probably synchrotron radiation from mildly relativistic electrons; energies in the range ∼0.1 to ∼1 MeV could account for the observed strong circular polarizations.With an expanding magnetic arch, source and magnetic-field movement are inseparable; the field remains a closed loop throughout the event. The MHD front probably moves largely along and the plasmoids between the open magnetic-field lines of unipolar regions or helmet structures. In the latter case it is the internal magnetic field – possibly toroidal – of the moving plasmoid that determines the polarization of the synchrotron radiation. A preliminary comparison of moving type IV sources with Newkirk-Altschuler maps of coronal magnetic fields shows suitably located closed loops for 2 events identified as expanding magnetic arches and unipolar open field lines along the path of a moving source identified as a plasmoid.

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