Global energetics of solar flares. VIII. The low-energy cutoff

Aschwanden, M. J., Kontar, E. P. and Jeffrey, N. L.S. (2019) Global energetics of solar flares. VIII. The low-energy cutoff. Astrophysical Journal, 881(1), 1. (doi:10.3847/1538-4357/ab2cd4)

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Abstract

One of the key problems in solar flare physics is the determination of the low-energy cut-off: the value that determines the energy of nonthermal electrons and hence flare energetics. We discuss different approaches to determine the low-energy cut-off in the spectrum of accelerated electrons: (i) the total electron number model, (ii) the time-of-flight model (based on the equivalence of the time-of-flight and the collisional deflection time), (iii) the warm target model of Kontar et al., and (iv) the model of the spectral cross-over between thermal and nonthermal components. We find that the first three models are consistent with a low-energy cutoff with a mean value of ≈10 keV, while the cross-over model provides an upper limit for the low-energy cutoff with a mean value of ≈21 keV. Combining the first three models we find that the ratio of the nonthermal energy to the dissipated magnetic energy in solar flares has a mean value of q E = 0.57 ± 0.08, which is consistent with an earlier study based on the simplified approximation of the warm target model alone (q E = 0.51 ± 0.17). This study corroborates the self-consistency between three different low-energy cutoff models in the calculation of nonthermal flare energies.

Item Type:Articles
Additional Information:This work was partially supported by NASA contracts NNX11A099G, NNG04EA00C (SDO/AIA), and NNG09FA40C (IRIS).
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kontar, Professor Eduard and Jeffrey, Dr Natasha
Authors: Aschwanden, M. J., Kontar, E. P., and Jeffrey, N. L.S.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:IOP Publishing
ISSN:0004-637X
ISSN (Online):1538-4357
Published Online:06 August 2019
Copyright Holders:Copyright © 2019 The American Astronomical Society
First Published:First published in Astrophysical Journal 881(1):1
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
631581Consolidated grant in solar and astrophysical plasmasLyndsay FletcherScience & Technology Facilities Council (STFC)ST/L000741/1S&E P&A - PHYSICS & ASTRONOMY