Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares

Simoes, P. J. A. and Kontar, E. P. (2013) Implications for electron acceleration and transport from non-thermal electron rates at looptop and footpoint sources in solar flares. Astronomy and Astrophysics, 551, A135. (doi: 10.1051/0004-6361/201220304)

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The interrelation of hard X-ray (HXR) emitting sources and the underlying physics of electron acceleration and transport presents one of the major questions in the high energy solar flare physics. Spatially resolved observations of solar flares often demonstrate the presence of well separated sources of bremsstrahlung emission, so-called coronal and foot-point sources. Using spatially resolved X-ray observations by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and recently improved imaging techniques, we investigate in detail the spatially resolved electron distributions in a few well observed solar flares. The selected flares can be interpreted as having a standard geometry with chromospheric HXR foot-point sources related to thick-target X-ray emission and the coronal sources characterised by a combination of thermal and thin-target bremsstrahlung. Using imaging spectroscopy technique, we deduce the characteristic electron rates and spectral indices required to explain the coronal and foot-points X-ray sources. We found that, during the impulsive phase, the electron rate at the loop-top is several times (a factor of 1.7-8) higher than at the foot-points. The results suggest sufficient number of electrons accelerated in the loop-top to explain the precipitation into the foot-points and implies electrons accumulation in the loop-top. We discuss these results in terms of magnetic trapping, pitch-angle scattering and injection properties. Our conclusion is that the accelerated electrons must be subject to magnetic trapping and/or pitch-angle scattering, keeping a fraction of the population trapped inside the coronal loops. These findings put strong constraints on the particle transport in the coronal source, and provide a quantitative limits on deka-keV electron trapping/scattering in the coronal source.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Simoes, Dr Paulo and Kontar, Professor Eduard
Authors: Simoes, P. J. A., and Kontar, E. P.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astronomy and Astrophysics
Publisher:EDP Sciences
ISSN (Online):1432-0746
Published Online:07 March 2013
Copyright Holders:Copyright © 2013 ESO
First Published:First published in Astronomy and Astrophysics 551:A135
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
542081Rolling Programme in Solar and Plasma AstrophysicsLyndsay FletcherScience & Technologies Facilities Council (STFC)ST/I001808/1P&A - PHYSICS & ASTRONOMY