Gyrosynchrotron emission from quasi-thermal electrons and applications to solar flares

Journal Article · Sat Dec 15 00:00:00 EST 1979 · Astrophys. J.; (United States)

DOI:https://doi.org/10.1086/157597· OSTI ID:5485843

Dulk, G A; Melrose, D B; White, S M

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 ..omega.. to approx.100approx. =/sub e/ and temperatures T/sub e/ to approx.10/sup 9/ 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 f/sup 2/ at low frequencies, maximizes as some frequency f/sub peak/, and falls very rapidly thereafter; this shape fits the observed spectra qualitatively. The optical deth tau of the source varies rapidly with f, with tau=1 at fapprox. =f/sub peak/. For T/sub e/> or approx. =10/sup 8/ we derive the relation f/sub peak/proportionalT/sub e//sup 0.7/ B, 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 T/sub e/approx. =2.3 x 10/sup 8/ K, Bapprox. =370 gauss, n/sub e/approx. =2 x 10/sup 9/ cm/sup -3/ and scale length Lapprox. =8600 km.

• Research Organization: Division of Radiophysics, CSIRO, Sydney, Australia; and Departent of Astro-Geophysics, University of Colorado, Boulder
• OSTI ID: 5485843
• Journal Information: Astrophys. J.; (United States), Vol. 234:3
• Country of Publication: United States
• Language: English

Related Subjects

71 CLASSICAL AND QUANTUM MECHANICS
GENERAL PHYSICS
SOLAR FLARES
SYNCHROTRON RADIATION
SOLAR X-RAY BURSTS
BOLTZMANN STATISTICS
ELECTRONS
ENERGY SPECTRA
HARMONICS
MAGNETIC FIELDS
PLASMA
RADIATION FLUX
SOLAR RADIOWAVE RADIATION
BREMSSTRAHLUNG
ELECTROMAGNETIC RADIATION
ELEMENTARY PARTICLES
FERMIONS
LEPTONS
OSCILLATIONS
RADIATIONS
RADIOWAVE RADIATION
SOLAR ACTIVITY
SOLAR RADIATION
SPECTRA
640104* - Astrophysics & Cosmology- Solar Phenomena