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Session 36 - Extragalactic X-Ray Sources.
Display session, Tuesday, January 14
Obscuration by cold matter is frequently observed in a variety of X-ray sources. With the improved sensitivity and energy resolution of the new generation of X-ray detectors, such as those aboard ASCA, it may not always be possible to neglect electron scattering for column densities much greater than \sim 10^23 \ cm^-2. We derive simple, approximate analytic expressions for a spherical geometry which enable the transmitted flux to be corrected for nonrelativistic Compton scattering. The method allows the use of arbitrary element abundances, photoelectric absorption cross-sections and input spectra and is computationally fast enough for use in a spectral fitting code. The approximations can be used for column densities up to \sim 5 \times 10^24 \ cm^-2. The maximum observed energy for which the approximations are valid depends on the column density and is \sim 18.5 keV for N_H = 10^23 \ cm^-2 and \sim 10 keV for N_H = 5 \times 10^24 \ cm^-2. The model provides a significantly improved description of the transmitted spectrum compared to the usual model in which only attenuation due to the absorption opacity is considered and scattering is neglected altogether. The latter leads to errors in the transmitted spectrum which can exceed an order of magnitude, especially around the Fe-K edge.
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