Jeffrey, N. L.S. , Fletcher, L. and Labrosse, N. (2017) Non-gaussian velocity distributions in solar flares from extreme ultraviolet lines: a possible diagnostic of ion acceleration. Astrophysical Journal, 836(1), (doi: 10.3847/1538-4357/836/1/35)
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Abstract
In a solar flare, a large fraction of the magnetic energy released is converted rapidly to the kinetic energy of non-thermal particles and bulk plasma motion. This will likely result in non-equilibrium particle distributions and turbulent plasma conditions. We investigate this by analyzing the profiles of high temperature extreme ultraviolet emission lines from a major flare (SOL2014-03-29T17:44) observed by the EUV Imaging Spectrometer (EIS) on Hinode. We find that in many locations the line profiles are non-Gaussian, consistent with a kappa distribution of emitting ions with properties that vary in space and time. At the flare footpoints, close to sites of hard X-ray emission from non-thermal electrons, the κ index for the Fe xvi 262.976 Å line at 3 MK takes values of 3–5. In the corona, close to a low-energy HXR source, the Fe xxiii 263.760 Å line at 15 MK shows κ values of typically 4–7. The observed trends in the κ parameter show that we are most likely detecting the properties of the ion population rather than any instrumental effects. We calculate that a non-thermal ion population could exist if locally accelerated on timescales ≤0.1 s. However, observations of net redshifts in the lines also imply the presence of plasma downflows, which could lead to bulk turbulence, with increased non-Gaussianity in cooler regions. Both interpretations have important implications for theories of solar flare particle acceleration.
Item Type: | Articles |
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Status: | Published |
Refereed: | Yes |
Glasgow Author(s) Enlighten ID: | Fletcher, Professor Lyndsay and Jeffrey, Dr Natasha and Labrosse, Dr Nicolas |
Authors: | Jeffrey, N. L.S., Fletcher, L., and Labrosse, N. |
College/School: | College of Science and Engineering > School of Physics and Astronomy |
Journal Name: | Astrophysical Journal |
Publisher: | American Astronomical Society |
ISSN: | 0004-637X |
ISSN (Online): | 1538-4357 |
Published Online: | 07 February 2017 |
Copyright Holders: | Copyright © 2017 American Astronomical Society |
First Published: | First published in Astrophysical Journal 2017 |
Publisher Policy: | Reproduced in accordance with the copyright policy of the publisher |
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