Positions and sizes of X-ray solar flare sources

Kontar, E.P. and Jeffrey, N.L.S. (2010) Positions and sizes of X-ray solar flare sources. Astronomy and Astrophysics, 513, (doi:10.1051/0004-6361/201014066)

Kontar, E.P. and Jeffrey, N.L.S. (2010) Positions and sizes of X-ray solar flare sources. Astronomy and Astrophysics, 513, (doi:10.1051/0004-6361/201014066)

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Abstract

<p><b>Aims:</b> The positions and source sizes of X-ray sources taking into account Compton backscattering (albedo) are investigated.</p> <p><b>Methods:</b> Using a Monte Carlo simulation of X-ray photon transport including photo-electric absorption and Compton scattering, we calculate the apparent source sizes and positions of X-ray sources at the solar disk for various source sizes, spectral indices and directivities of the primary source.</p> <p><b>Results:</b> We show that the albedo effect can alter the true source positions and substantially increase the measured source sizes. The source positions are shifted by up to ~0.5” radially towards the disk centre and 5 arcsec source sizes can be two times larger even for an isotropic source (minimum albedo effect) at 1 Mm above the photosphere. The X-ray sources therefore should have minimum observed sizes, and thus their FWHM source size (2.35 times second-moment) will be as large as ~7” in the 20-50 keV range for a disk-centered point source at a height of 1 Mm (~1.4”) above the photosphere. The source size and position change is greater for flatter primary X-ray spectra, a stronger downward anisotropy, for sources closer to the solar disk centre, and between the energies of 30 and 50 keV.</p> <p><b>Conclusions:</b> Albedo should be taken into account when X-ray footpoint positions, footpoint motions or source sizes from e.g. RHESSI or Yohkoh data are interpreted, and we suggest that footpoint sources should be larger in X-rays than in either optical or EUV ranges.</p>

Item Type:Articles
Additional Information:L2
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kontar, Dr Eduard and Jeffrey, Dr Natasha
Authors: Kontar, E.P., and Jeffrey, N.L.S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astronomy and Astrophysics
Publisher:EDP Sciences
ISSN:0004-6361
ISSN (Online):1432-0746
Published Online:14 April 2010
Copyright Holders:Copyright © 2010 EDP Sciences
First Published:First published in Astronomy and Astrophysics 513(L2)
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
398461Acceleration, propagation and emission of energetic particles from the sun to the earthEduard KontarParticle Physics & Astronomy Research Council (PPARC)PP/C001656/1Physics and Astronomy
465931Solar, stellar and cosmological plasmas: a synthesis of data, modelling and theory.Declan DiverScience & Technologies Facilities Council (STFC)ST/F002149/1Physics and Astronomy