The sub-arcsecond hard x-ray structure of loop footpoints in a solar flare

Kontar, E.P. , Hannah, I.G. , Jeffrey, N.L.S. and Battaglia, M. (2010) The sub-arcsecond hard x-ray structure of loop footpoints in a solar flare. Astrophysical Journal, 717(1), pp. 250-256. (doi: 10.1088/0004-637X/717/1/250)

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The newly developed X-ray visibility forward fitting technique is applied to the RHESSI data of a limb flare to investigate the energy and height dependence on sizes, shapes, and position of hard X-ray (HXR) chromospheric footpoint sources. This provides information about the electron transport and chromospheric density structure. The spatial distribution of two footpoint X-ray sources is analyzed using PIXON, Maximum Entropy Method, CLEAN, and visibility forward fit algorithms at nonthermal energies from ~20 to ~200 keV. We report, for the first time, the vertical extents and widths of HXR chromospheric sources measured as a function of energy for a limb event. Our observations suggest that both the vertical and horizontal sizes of footpoints are decreasing with energy. Higher energy emission originates progressively deeper in the chromosphere, consistent with downward flare accelerated streaming electrons. The ellipticity of the footpoints grows with energy from ~0.5 at ~20 keV to ~0.9 at ~150 keV. The positions of X-ray emission are in agreement with an exponential density profile of scale height ~150 km. The characteristic size of the HXR footpoint source along the limb decreases with energy, suggesting a converging magnetic field in the footpoint. The vertical sizes of X-ray sources are inconsistent with simple collisional transport in a single density scale height but can be explained using a multi-threaded density structure in the chromosphere.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Jeffrey, Dr Natasha and Hannah, Dr Iain and Battaglia, Dr Marina and Kontar, Professor Eduard
Authors: Kontar, E.P., Hannah, I.G., Jeffrey, N.L.S., and Battaglia, M.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Published Online:10 June 2010
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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