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. ISSN 0004-6361 (doi:10.1051/0004-6361:20066689)
Publisher's URL: http://dx.doi.org/10.1051/0004-6361:20066689
Aims: 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.
Methods: Using Ramaty High Energy Solar Spectroscopic Imager (RHESSI) flare data we perform a statistical analysis of spatially integrated spectra and positions of solar flares.
Results: 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.
|Keywords:||Sun: flares, sun: X-rays, gamma rays, sun: particle emission, scattering, techniques: spectroscopic.|
|Glasgow Author(s):||Kontar, Dr Eduard and Brown, Prof 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|
|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|