Influence of photospheric back-scatter on flare hard x-ray diagnostics.

Alexander, Robert Calum (2010) Influence of photospheric back-scatter on flare hard x-ray diagnostics. PhD thesis, University of Glasgow.

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 amp; 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).

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Keywords: Solar Flare Spectroscopy, Solar Flare Hard X-Ray Diagnostics, Solar Photospheric Back-Scatter, Compton Back-Scatter, Albedo, Green’s Function Albedo Correction, Energy Dependent Anisotropic Primary Photon Emission, Hemispheric Eddington Anisotropic Approximation, Photon Spectra, Electron Spectra
• Subjects: Q Science > QB Astronomy; Q Science > QC Physics
• Colleges/Schools: College of Science and Engineering > School of Physics and Astronomy
• Supervisor's Name: Brown, Professor John C.
• Date of Award: 2010
• Depositing User: Mr R. Calum Alexander
• Unique ID: glathesis:2010-1707
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 07 Apr 2010
• Last Modified: 25 Jun 2015 13:45
• URI: https://theses.gla.ac.uk/id/eprint/1707