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Astron. Astrophys. 340, 277-286 (1998)

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On the role of beam driven return current instabilities in white-light flares

S.A. Matthews 1, J.C. Brown 2 and L. van Driel-Gesztelyi 3, 4

1 Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Surrey RH5 6NT, UK (sam@mssl.ucl.ac.uk)
2 Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ, UK (john@astro.gla.ac.uk)
3 DASOP, Observatoire de Paris, F-92195 Meudon Principal Cedex, France
4 Konkoly Observatory, Pf 67, H-1525 Budapest, Hungary (lvandrie@mesioq.obspm.fr)

Received 9 July 1998 / Accepted 18 September 1998

Abstract

It has been shown previously that the low ionization levels in the deep chromosphere of solar flares can cause the return current driven by a thick target electron beam to be unstable to ion aoustic wave generation, contrary to conventional wisdom. We investigate, using Yohkoh data, the possibility that anomalous heating as a result of this instability is capable of producing sufficient heating, in the right places at the right times, to account for the enhanced continuum emission actually observed in white-light flares. The Soft X-ray Telescope (SXT) onboard Yohkoh incorporates an aspect camera which, prior to its failure in 1992, provided white-light images at 431 nm with a bandpass of 3 nm. A number of white-light flares were observed during its operational lifetime for which there was coincident hard X-ray data from the Hard X-ray Telescope (HXT), providing suitable candidates for study. Four such events are discussed, and the model found to be viable.

Key words: Sun: activity – Sun: flares – Sun: X-rays, gamma rays

Send offprint requests to: S.A. Matthews

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© European Southern Observatory (ESO) 1998

Online publication: November 3, 1998
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