X–ray spectra transmitted through Compton–thick absorbers
نویسندگان
چکیده
The presence of large amount of “cold” (i.e. not much ionized, and substantially opaque in X–rays) matter around Active Galactic Nuclei is now a well established fact. For all Seyfert 2 galaxies observed in X–rays so far there is evidence for absorption in excess of the Galactic one. In a significant fraction of them, the column density of the absorbing matter exceeds 10 cm−2 (Maiolino et al. 1998), and the matter is therefore optically thick to Compton scattering. In a few objects, like NGC 1068 (Matt et al. 1997), the column density is so high that the X–ray photons cannot escape even in hard X–rays, being trapped in the matter, downscattered to energies where photoelectric absorption dominates, and eventually destroyed. In other cases, like NGC 4945 (Iwasawa et al. 1993; Done et al. 1996), Mrk 3 (Cappi et al. 1999) and the Circinus Galaxy (Matt et al. 1999), the column density is a few×1024 cm−2, so permitting the transmission of a significant fraction of X–ray photons, many of them escaping after one or more scatterings. To properly model transmission through absorbers with these intermediate column densities, is therefore
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