Relationship between hard and soft X-ray emission components of a solar flare

Guo, J., Liu, S., Fletcher, L. and Kontar, E.P. (2011) Relationship between hard and soft X-ray emission components of a solar flare. Astrophysical Journal, 728(1), (doi:10.1088/0004-637X/728/1/4)

Guo, J., Liu, S., Fletcher, L. and Kontar, E.P. (2011) Relationship between hard and soft X-ray emission components of a solar flare. Astrophysical Journal, 728(1), (doi:10.1088/0004-637X/728/1/4)

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Abstract

X-ray observations of solar flares routinely reveal an impulsive high-energy and a gradual low-energy emission component, whose relationship is one of the key issues of solar flare study. The gradual and impulsive emission components are believed to be associated with, respectively, the thermal and nonthermal components identified in spectral fitting. In this paper, a prominent ~50 s hard X-ray (HXR) pulse of a simple GOES class C7.5 flare on 2002 February 20 is used to study the association between high-energy, non-thermal, and impulsive evolution, and low-energy, thermal, and gradual evolution. We use regularized methods to obtain time derivatives of photon fluxes to quantify the time evolution as a function of photon energy, obtaining a break energy between impulsive and gradual behavior. These break energies are consistent with a constant value of ~11 keV in agreement with those found spectroscopically between thermal and non-thermal components, but the relative errors of the former are greater than 15% and much greater than the few percent errors found from the spectral fitting. These errors only weakly depend on assuming an underlying spectral model for the photons, pointing to the current data being inadequate to reduce the uncertainties rather than there being a problem associated with an assumed model. The time derivative method is used to test for the presence of a "pivot energy" in this flare. Although these pivot energies are marginally consistent with a constant value of ~9 keV, its values in the HXR rise phase appear to be lower than those in the decay phase. Assuming that electrons producing the high-energy component have a power-law distribution and are accelerated from relatively hot regions of a background plasma responsible for the observed thermal component, a low limit is obtained for the low-energy cutoff. This limit is always lower than the break and pivot energies and is located in the tail of the Maxwellian distribution of the thermal component.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Kontar, Dr Eduard and Fletcher, Professor Lyndsay and Guo, Ms Jingnan and Liu, Dr Siming
Authors: Guo, J., Liu, S., Fletcher, L., and Kontar, E.P.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
ISSN:0004-637X
Published Online:13 January 2011
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