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Astron. Astrophys. 320, L13-L16 (1997)

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Letter to the Editor

Return current effects on hard X-ray and microwave emission produced by electron beams in solar flares

V.V.Zharkova 1 and D.V.Syniavskii 2

1 Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, Scotland, U.K.
2 Physics Department, Kiev University, Kiev, 252022, UKRAINE

Received 24 September 1996 / Accepted 21 January 1997


Electron beam distribution functions, found from a joint solution of the kinetic and electric current conservation equations for an electron beam in converging magnetic field, are used for the calculations of resulting hard X-ray bremsstrahlung fluxes for beams with different parameters. X-ray fluxes are shown to have non-monotonic energy distributions with the flux depression (dip) at 20-25 keV, caused by the effect of an electric current on the beam electron distributions, with spectral indices before the dip higher by 1-1.5 units than after it. These effects can explain surprisingly well the observational discrepancies in spectral indices and total energy fluxes, detected from SMM and Yohkoh hard X-ray observations in different energy bands.

Key words: Sun: flares – Sun: x-rays – plasmas – electron beams

Send offprint requests to: V.V.Zharkova

© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998