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D. Alexander (Rice University), K.G. McClements (UKAEA Culham)
Chromospheric hard X-ray emission in a solar flare generally occurs in two magnetically connected 'footpoint' regions. Recent spatially-resolved hard X-ray observations carried out using the RHESSI spacecraft have shown that the ratio of total X-ray fluxes from two such footpoints is time-dependent and demonstrates a weak but detectable energy-dependence. We use a Fokker-Planck code to identify possible scenarios that could reproduce the observed dependence of footpoint asymmetry on time and energy. The code, which we have benchmarked against analytical results in the limit of collisionless precipitation from a symmetric flaring loop, includes collisional friction and pitch angle scattering, asymmetric magnetic mirroring, and a source term that can be prescribed arbitrarily. Using this model, we examine in particular whether the observed imbalance in hard X-ray emission from the two footpoints in a flare can be attributed primarily to asymmetry in the loop magnetic structure or asymmetry in the acceleration process.
This work was funded partly by NASA (NAS5-02048) and by the United Kingdom Engineering and Physical Sciences Research Council.
The author(s) of this abstract have provided an email address for comments about the abstract: dalex@rice.edu
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Bulletin of the American Astronomical Society, 36 #2
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