The role of energy diffusion in the deposition of energetic electron energy in solar and stellar flares

Jeffrey, N. L.S. , Kontar, E. P. and Fletcher, L. (2019) The role of energy diffusion in the deposition of energetic electron energy in solar and stellar flares. Astrophysical Journal, 880(2), 136. (doi:10.3847/1538-4357/ab2764)

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Abstract

During solar flares, a large fraction of the released magnetic energy is carried by energetic electrons that transfer and deposit energy in the Sun's atmosphere. Electron transport is often approximated by a cold thick-target model, assuming that electron energy is much larger than the temperature of the ambient plasma, and electron energy evolution is modeled as a systematic loss. Using kinetic modeling of electrons, we reevaluate the transport and deposition of flare energy. Using a full collisional warm-target model (WTM), we account for electron thermalization and for the properties of the ambient coronal plasma such as its number density, temperature and spatial extent. We show that the deposition of nonthermal electron energy in the lower atmosphere is highly dependent on the properties of the flaring coronal plasma. In general, thermalization and a reduced WTM energy loss rate leads to an increase of nonthermal energy transferred to the chromosphere, and the deposition of nonthermal energy at greater depths. The simulations show that energy is deposited in the lower atmosphere initially by high-energy nonthermal electrons, and later by lower energy nonthermal electrons that partially or fully thermalize in the corona, over timescales of seconds, unaccounted for in previous studies. This delayed heating may act as a diagnostic of both the injected nonthermal electron distribution and the coronal plasma, vital for constraining flare energetics.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Fletcher, Professor Lyndsay and Jeffrey, Dr Natasha and Kontar, Professor Eduard
Authors: Jeffrey, N. L.S., Kontar, E. P., and Fletcher, L.
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:02 August 2019
Copyright Holders:Copyright © 2019 American Astronomical Society
First Published:First published in Astrophysical Journal 880(2): 136
Publisher Policy:Reproduced in accordance with the publisher copyright policy

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
728901Consolidated Grant in Solar PhysicsLyndsay FletcherScience & Technology Facilities Council (STFC)ST/P000533/1S&E P&A - PHYSICS & ASTRONOMY