Use this URL to cite or link to this record in EThOS: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.513245
Title: Influence of photospheric back-scatter on flare hard x-ray diagnostics
Author: Alexander, Robert Calum
Awarding Body: University of Glasgow
Current Institution: University of Glasgow
Date of Award: 2010
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Abstract:
In this thesis I present the results of studies on the influence of solar photospheric back–scatter on Hard X–Ray (HXR) flare diagnostics. Specifically the thesis presented is concerned with the effect of back–scatter photons upon the morphology of the Hard X–Ray photon spectrum and its effect on the inferred parent electron spectrum. I present a theoretical investigation into Compton reflected HXR photons, known as the photospheric Albedo, and explore the effect of photospheric albedo on observations of global flare hard X-ray spectra for isotropic emission. I examine, for the Kramers cross-section, the consequences of ignoring the albedo correction in using observed spectra to infer flare source electron spectra for thin and thick target interpretations and show that the effects are very significant in terms of inferred spectral shape, especially for hard spectra. I extend this investigation to consider the effect of the photospheric albedo on observations of global flare hard X-ray spectra for anisotropic primary photon emission by examining, for the Kramers cross-section, the consequences of ignoring the albedo correction in using observed spectra to infer flare source electron spectra for thin and thick target interpretations. For an energy dependent multiplier α I find that the results for anisotropic emission are similar in shape to isotropic emission when I assume a linear model for the anisotropy. I then explore two complementary techniques for determining the Compton back-scattered component of the observed photon spectrum using a model independent Greens function approach. The first is a matrix based technique developed by Kontar & Brown (2006) which I extend to include anisotropic primary photon emission using an Eddington hemispheric approach along with an empirical fit to published data. The second is a full radiative transfer Greens function approach developed by Poutanen et al. (1996) which I also extend to include anisotropic primary photon emission again using an empirical fit to published data. In both cases I investigate how anisotropic primary photon emission effects the observed photon spectrum by studying the differences in the size and shape of the albedo. In the final chapter I use the results from the anisotropic Eddington hemispheric Greens function approach and the anisotropic full radiative transfer Greens function approach to investigate the findings published in Kontar & Brown (2006) using the Stereoscopic electron spectroscopy technique. I conclude from the results of this comparison that doing a full anisotropic scattering properly does not fundamentally change the findings of Kontar and Brown which are specifically that the electron distribution is nearly isotropic to such a degree of confidence that it casts doubt on models which are based upon beaming such as the collisional thick target (Brown 1971).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID: uk.bl.ethos.513245  DOI: Not available
Keywords: QB Astronomy ; QC Physics
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