Hard x-ray emission and mass motion in solar flares

McClymont, Alexander N. (1976) Hard x-ray emission and mass motion in solar flares. PhD thesis, University of Glasgow.

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Solar flares are perhaps the most remarkable transient events within the solar system. A century of observation has done little to elucidate their true nature. Their secrets are hidden even from the sophisticated satellite experiments which have kept up an intensive surveillance for the last decade. These experiments have, however, produced an indigestible mass of data. From these we must try to synthesis an overall picture of the flare and identify the physical processes responsible. In this thesis two aspects of the flare problem are considered. The first concerns hard X-ray emission during the impulsive phase of the flare. The electron trap model of the hard X-ray source is analysed in detail and the predicted directivity and polarisation of its emission found to be compatible with hard X-ray observational data. Secondly, a self-consistent model of the soft X-ray flare is developed. Mass motion, which has previously been ignored in such models, is shown to be of vital importance. In Chapter I, the observational evidence concerning all types of flare emission is summarised. The coherency of a picture of the flare in which energetic electrons play a central part is pointed out and the significance of hard X-ray emission as an indicator of the properties of these electrons noted. Current hard X-ray source models are described in Chapter II and their predictions for the flare X-radiation outlined. Other topics of importance to the hard X-ray problem - bremsstrahlung radiation, the albedo effect and modulation of the X-ray flux - are also discussed here. Finally, the predictions of the source models are compared with observation and important areas of experimental and theoretical research suggested. The electron trap hard X-ray source model is analysed in Chapter III. This model, whose properties have only been guessed at until now, postulates that high energy electrons are trapped in a coronal magnetic arch where they emit bremsstrahlung radiation while decaying collisionally on the time scale of the hard X-ray burst decay. Directivity and polarisation of the emission are predicted for a variety of trapped electron distributions over energy and pitch angle. Predicted properties of the hard X-ray emission are presented in Chapters IV and V. Chapter IV is concerned with the total X-ray flux from the trap while Chapter V deals with some aspects of the spatially resolved emission, in particular the predicted "behind-the- limb" X-ray flux. In both chapters, results are compared with the observational data available and observations which could help to discriminate between this and other source models suggested. In Chapter VI a model of the soft X-ray flare is developed. The model consists of a high density coronal filament into the centre of which energy is injected during the impulsive phase of the flare. First, the potential importance of mass motion in this situation is demonstrated by dimensional analysis. Then a numerical treatment of the fluid dynamic equations is developed. Computational results describing the evolution of the filament, under a variety of conditions, are presented in Chapter VII. Conclusions drawn from the dimensional analysis are vindicated and deeper insight into the energy transport processes operating in the filament obtained. The soft X-ray differential emission measure is examined and it is suggested that the form is compatible with that inferred from observation.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Subjects: Q Science > QB Astronomy
Colleges/Schools: College of Science and Engineering
Supervisor's Name: Brown, Dr. John C.
Date of Award: 1976
Depositing User: Mrs Marie Cairney
Unique ID: glathesis:1976-30720
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 07 Aug 2018 14:57
Last Modified: 15 Aug 2019 16:06
URI: http://theses.gla.ac.uk/id/eprint/30720
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