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Session 1 - Chromosphere, Corona, Flares.
Display session, Friday, June 27
Ballroom B, Chair: Charles Kankelborg

[1.58] Inversion of Thick-target Bremsstrahlung Spectra from Nonuniformly Ionized Plasmas

A. G. Emslie (Dept. of Physics, UAH), J. C. Brown, G. K. McArthur, R. K. Barrett, S. W. McIntosh (Dept. of Physics and Astronomy, University of Glasgow)

The energy loss rate of bremsstrahlung-producing electrons is strongly dependent on the ionization level of the target with which they interact. Electrons injected from the corona toward the chromosphere suffer reduced energy losses, and therefore become more efficient at bremsstrahlung production, when they enter the near-neutral chromospheric layers. Thus the electron spectrum inferred from a uniform target model (as hitherto universally applied to data) causes a serious overestimate of the number of injected electrons, particularly at the low energies appropriate to the electrons as they enter the chromosphere. We here demonstrate how to derive the correct injected electron spectrum from that derived from a uniform target model. Significantly, we find that the correct spectrum is not unique, even for perfect (noise-free) hard X-ray data. The implications of this result for the interpretation of hard X-ray spectral data, and a possible method of determining the location of the corona/chromosphere ionization jump using information on the evolution of the hard X-ray spectrum throughout the flare, are discussed.


Program listing for Friday