The gyrosynchrotron emission from quasi-thermal electrons and applications to solar flares

Details The gyrosynchrotron emission from quasi-thermal electrons and applications to solar flares The gyrosynchrotron emission from quasi-thermal electrons and applications to solar flares

Dec 1979

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1979apj...234.1137d&link_type=abstract

Astrophysical Journal, Part 1, vol. 234, Dec. 15, 1979, p. 1137-1147.

Other

51

Electron Energy, Solar Flares, Solar Radio Emission, Synchrotron Radiation, Energy Distribution, Maxwell-Boltzmann Density Function, Solar Electrons, X Ray Spectra

Scientific paper

We present theoretical results on the gyrosynchrotron radiation from electrons with a Maxwellian energy distribution. We review the analytical expressions for the gyromagnetic absorption coefficient and find two which cover the range of interest for microwave emission from solar flares, i.e., frequencies ω to ∼100Ωe and temperatures Te to ∼109 K. Numerical calculations are used to check the analytic expressions and to derive simplified empirical formulae which relate the observable characteristics of the radiation to the temperature and magnetic field in the source.
We apply the results to the sources of impulsive microwave and hard X-ray bursts from solar flares. For an isothermal source the theory predicts a microwave spectrum where the flux density rises as f2 at low frequencies, maximizes as some frequency fpeak, and falls very rapidly thereafter; this shape fits the observed spectra qualitatively. The optical depth τ of the source varies rapidly with f, with τ = 1 at f ≍ fpeak. For Te ≳ 108 K we derive the relation fpeak ∝ Te0.7B, which allows a direct estimate of the magnetic field B in the impulsive burst source if the temperature is known-for instance, from hard X-ray observations. For the impulsive burst of 1972 May 18, reported by Hoyng and Stevens, we find that the microwave and hard X-ray data are well fitted by a model source with Te ≍ 2.3 × 108 K, B ≍ 370 gauss, ne 2 × 109 cm-3, and scale length L ≍ 8600 km.

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