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Nonuniform Target Ionisation and Fitting Thick Target Electron Injection Spectra to RHESSI Data View all abstracts by submitter

Eduard Kontar   Submitted: 2003-03-26 15:02

Past analysis of flare Hard X-Ray (HXR) spectra have largely ignored the effect of nonuniform ionisation along the electron paths in the thick target model, though it is very significant for well-resolved spectra. The inverse problem (photon spectrum to electron injection spectrum {cal F}_0(E_0)) is disturbingly non-unique. However, we show that it is relatively simple to allow for the effect in forward fitting of parametric models of {cal F}_0(E_0) and provide an expression to evaluate it for the usual single power law form of {cal F}_0(E_0). The expression involves the column depth N_* of the transition region in the flare loop as one of the parameters so data fitting can enable derivation of N_* (and its evaporative evolution) as part of the fitting procedure. The fit to RHESSI data on four flares for a single power law {cal F}_0(E_0) is much improved when ionisation structure is included compared to when the usual fully ionised approximation is used. This removes the need, in these events at least, to invoke broken power-laws, or other forms, of the acceleration spectrum {cal F}_0(E_0) to explain the observed photon spectrum.

Authors: E.P. Kontar, J.C. Brown, and G. K. McArthur
Projects: RHESSI

Publication Status: Solar Physics, (in press)
Last Modified: 2005-12-07 05:18
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