Astronomy and Astrophysics – Astrophysics
Scientific paper
Sep 2002
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2002phdt........34s&link_type=abstract
Thesis (PhD). THE UNIVERSITY OF ALABAMA IN HUNTSVILLE, Source DAI-B 63/03, p. 1411, Sep 2002, 189 pages.
Astronomy and Astrophysics
Astrophysics
2
Scientific paper
Impulsive solar flares occupy a unique position in the realm of energetic transient astrophysical phenomena, releasing up to 1032 ergs of energy over times that range from a few minutes to a few hours. A large fraction of the energy is contained in suprathermal particles that remain trapped at the sun or escape into the corona. A major signature of a solar flare is the hard X-ray emission generated by ˜100 keV electrons which interact with the ambient plasma to produce continuum radiation that ranges from radio, to microwave, soft X-rays and occasionally gamma-rays. We investigate time-dependent solar flare electron acceleration by large-scale sub-Dreicer fields, taking into account spatial transport, current closure, Coulomb collisions, and plasma waves. In this process, the particles are energized directly out of the thermal coronal plasma, where they can produce hard X-rays. We show that a bump-on-tail distribution readily develops if the current closure is localized near the ends of the current channel and we study the resultant wave-particle interactions. We then incorporate Joule heating and thermal conduction to explore the temperature evolution of the electron distribution. We study the conditions under which electric fields can produce the hard X-ray inferred fluxes of >20 keV electrons. We are able to successfully fit the high-energy hard X-ray spectrum from the 1980 June 27 solar flare using the numerically calculated hard X-ray spectrum generated from a solar flare that contained a superpositioning of filaments with different lengths and densities.
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