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)

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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