The effect of wave generation on HXR bremsstrahlung spectra from flare thick-target beams

Haydock, E.L., Brown, J.C., Conway, A.J. and Emslie, A.G. (2001) The effect of wave generation on HXR bremsstrahlung spectra from flare thick-target beams. Solar Physics, 203(2), 355 -369. (doi: 10.1023/A:1013389621784)

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Publisher's URL: http://dx.doi.org/10.1023/A:1013389621784

Abstract

Fast electrons in the solar atmosphere are detected by their hard X-ray bremsstrahlung and by type III radio bursts caused by `bump-on-tail' plasma wave generation. This paper investigates empirically the effect of wave generation on the HXR spectrum. Purely collisional propagation of an electron beam generates a bump in the distribution function, due to stopping of low-velocity electrons. The consequent positive gradient means there is a possibility of wave generation, production of type III radio bursts, and energy redistribution of the electron beam. We have represented this relaxation parametrically and calculated the global bremsstrahlung HXR emission spectrum. We show that for a range of relaxed forms, with different local electron spectral shapes, the bremsstrahlung spectrum integrated over the whole target is identical in shape to the purely collisionally evolved beam. Our results show that spatially integrated HXR spectral measurements would be unable to distinguish between the presence or absence of relaxation effects. Only spatially resolved hard X-ray spectra, such as anticipated from the HESSI mission, will be able to remove this ambiguity in HXR diagnostics of beam relaxation.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Brown, Professor John
Authors: Haydock, E.L., Brown, J.C., Conway, A.J., and Emslie, A.G.
Subjects:Q Science > QB Astronomy
Q Science > QC Physics
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Solar Physics
ISSN:0038-0938

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