The emission measure distribution of impulsive phase flare footpoints

Graham, D.R., Hannah, I.G. , Fletcher, L. and Milligan, R.O. (2013) The emission measure distribution of impulsive phase flare footpoints. Astrophysical Journal, 767(1), Art. 83. (doi:10.1088/0004-637X/767/1/83)

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Abstract

The temperature distribution of the emitting plasma is a crucial constraint when studying the heating of solar flare footpoints. However, determining this for impulsive phase footpoints has been difficult in the past due to insufficient spatial resolution to resolve the footpoints from the loop structures, and a lack of spectral and temporal coverage. We use the capabilities of Hinode/Extreme Ultraviolet Imaging Spectrometer to obtain the first emission measure distributions (EMDs) from impulsive phase footpoints in six flares. Observations with good spectral coverage were analyzed using a regularized inversion method to recover the EMDs. We find that the EMDs all share a peak temperature of around 8 MK, with lines formed around this temperature having emission measures (EMs) peaking between 1028 and 1029 cm–5, indicating a substantial presence of plasma at very high temperatures within the footpoints. An EMD gradient of EM(T) ~ T is found in all events. Previous theoretical work on EM gradients shows this to be consistent with a scenario in which the deposited flare energy directly heats only the top layer of the flare chromosphere, while deeper layers are heated by conduction.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay and Hannah, Dr Iain
Authors: Graham, D.R., Hannah, I.G., Fletcher, L., and Milligan, R.O.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:Institute of Physics on behalf of American Astronomical Society
ISSN:0004-637X
ISSN (Online):1538-4357
Published Online:28 March 2013
Copyright Holders:Copyright © 2013 American Astronomical Society
First Published:First published in Astrophysical Journal 767(1):Art. 83
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