A TRACE white light and RHESSI hard X-ray study of flare energetics

Fletcher, L. , Hannah, I.G. , Hudson, H.S. and Metcalf, T.R. (2007) A TRACE white light and RHESSI hard X-ray study of flare energetics. Astrophysical Journal, 656(2), pp. 1187-1196. (doi: 10.1086/510446)

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In this paper we investigate the formation of the white-light (WL) continuum during solar flares and its relationship to energy deposition by electron beams inferred from hard X-ray emission. We analyze nine flares spanning GOES classifications from C4.8 to M9.1, seven of which show clear cospatial RHESSI hard X-ray and TRACE WL footpoints. We characterize the TRACE WL/UV continuum energy under two simplifying assumptions: (1) a blackbody function, or (2) a Paschen-Balmer continuum model. These set limits on the energy in the continuum, which we compare with that provided by flare electrons under the usual collisional thick-target assumptions. We find that the power required by the white-light luminosity enhancement is comparable to the electron beam power required to produce the HXR emission only if the low-energy cutoff to the spectrum is less than 25 keV. The bulk of the energy required to power the white-light flare (WLF) therefore resides at these low energies. Since such low-energy electrons cannot penetrate deep into a collisional thick target, this implies that the continuum enhancement is due to processes occurring at moderate depths in the chromosphere.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Hudson, Dr Hugh and Fletcher, Professor Lyndsay and Hannah, Dr Iain
Authors: Fletcher, L., Hannah, I.G., Hudson, H.S., and Metcalf, T.R.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
ISSN (Online):1538-4357

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