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)

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, Professor 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 Code	Award No	Project Name	Principal Investigator	Funder's Name	Funder Ref	Lead Dept
39846	1	Acceleration, propagation and emission of energetic particles from the sun to the earth	Eduard Kontar	Particle Physics & Astronomy Research Council (PPARC)	PP/C001656/1	Physics and Astronomy
46593	1	Solar, stellar and cosmological plasmas: a synthesis of data, modelling and theory.	Declan Diver	Science & Technologies Facilities Council (STFC)	ST/F002149/1	Physics and Astronomy