Flare ribbon energetics in the early phase of an SDO flare

Fletcher, L. , Hannah, I.G. , Hudson, H.S. and Innes, D.E. (2013) Flare ribbon energetics in the early phase of an SDO flare. Astrophysical Journal, 771(2), pp. 1-3. (doi: 10.1088/0004-637X/771/2/104)

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The sites of chromospheric excitation during solar flares are marked by extended extreme ultraviolet ribbons and hard X-ray (HXR) footpoints. The standard interpretation is that these are the result of heating and bremsstrahlung emission from non-thermal electrons precipitating from the corona. We examine this picture using multi-wavelength observations of the early phase of an M-class flare SOL2010-08-07T18:24. We aim to determine the properties of the heated plasma in the flare ribbons, and to understand the partition of the power input into radiative and conductive losses. Using GOES, SDO/EVE, SDO/AIA, and RHESSI, we measure the temperature, emission measure (EM), and differential emission measure of the flare ribbons, and deduce approximate density values. The non-thermal EM, and the collisional thick target energy input to the ribbons are obtained from RHESSI using standard methods. We deduce the existence of a substantial amount of plasma at 10 MK in the flare ribbons, during the pre-impulsive and early-impulsive phase of the flare. The average column EM of this hot component is a few times 1028 cm–5, and we can calculate that its predicted conductive losses dominate its measured radiative losses. If the power input to the hot ribbon plasma is due to collisional energy deposition by an electron beam from the corona then a low-energy cutoff of ~5 keV is necessary to balance the conductive losses, implying a very large electron energy content. Independent of the standard collisional thick-target electron beam interpretation, the observed non-thermal X-rays can be provided if one electron in 103-104 in the 10 MK (1 keV) ribbon plasma has an energy above 10 keV. We speculate that this could arise if a non-thermal tail is generated in the ribbon plasma which is being heated by other means, for example, by waves or turbulence.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay and Hannah, Dr Iain and Hudson, Dr Hugh
Authors: Fletcher, L., Hannah, I.G., Hudson, H.S., and Innes, D.E.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:IOP Publishing for the American Astronomical Society
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2014 The American Astronomical Society
First Published:First published in Astrophysical Journal 771(2):1-3
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
497221Sub-arcsecond X-ray chromospheric density and magnetic field measurementsEduard KontarLeverhulme Trust (LEVERHULME)F/00179/AYP&A - PHYSICS & ASTRONOMY
537641High Energy Solar Physics Data in Europe HESPELyndsay FletcherEuropean Commission (EC)UNSPECIFIEDP&A - PHYSICS & ASTRONOMY