Hard X-ray spectra and positions of solar flares observed by RHESSI: photospheric albedo, directivity and electron spectra

Kašparová, J., Kontar, E.P. and Brown, J.C. (2007) Hard X-ray spectra and positions of solar flares observed by RHESSI: photospheric albedo, directivity and electron spectra. Astronomy and Astrophysics, 466, pp. 705-712. (doi:10.1051/0004-6361:20066689)

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Abstract

<p><b>Aims</b>: We investigate the signature of the photospheric albedo contribution in solar flare hard X-ray spectra, the effect of low energy cutoffs in electron spectra, and the directivity of hard X-ray emission.</p> <p><b>Methods</b>: Using Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flare data we perform a statistical analysis of spatially integrated spectra and positions of solar flares.</p> <p><b>Results</b>: We demonstrate clear centre-to-limb variation of photon spectral indices in the 15-20 keV energy range and a weaker dependency in the 20-50 keV range which is consistent with photospheric albedo as the cause. The results also suggest that low-energy cutoffs sometimes inferred in mean electron spectra are an artefact of albedo. We also derive the anisotropy (ratio of downward/observer directed photons) of hard X-ray emission in the 15-20 keV range for various heliocentric angles.</p>

Item Type:Articles
Keywords:Sun: flares, sun: X-rays, gamma rays, sun: particle emission, scattering, techniques: spectroscopic.
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kontar, Professor Eduard and Brown, Professor John
Authors: Kašparová, J., Kontar, E.P., and Brown, J.C.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astronomy and Astrophysics
Publisher:EDP Sciences
ISSN:0004-6361
Copyright Holders:Copyright © 2007 EDP Sciences
First Published:First published in Astronomy and Astrophysics 466:705-712
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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