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

Journal Article · Sat Dec 15 04:00:00 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), Journal Name: Astrophys. J.; (United States) Vol. 234:3; ISSN ASJOA
• Country of Publication: United States
• Language: English

Related Subjects

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