The effect of wave generation on HXR bremsstrahlung spectra from flare thick-target beams |
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Authors: | Haydock EL Brown JC Conway AJ Emslie AG |
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Institution: | (1) Department of Physics and Astronomy, University of Glasgow, G12 8QQ, U.K;(2) The Open University, Milton Keynes, MK7 6AA, U.K. |
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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. |
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Keywords: | |
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