Effect of X-ray spectra of Seyfert galaxies on the cosmic X-ray background.

Ginga observations of five Seyfert 1 galaxies have revealed that their X-ray spectra are not described by a single power law, but have an absorption-like feature at the energy of several to 10 keV. This feature is probably explained by the absorption of very thick cold matter covering about half of the central source. This interpretation leads to a flat slope spectrum above 10 keV. The authors find that the superposition of such spectra can reproduce the 3 - 100 keV spectrum of the cosmic X-ray background (XRB) provided that the spectra of Seyfert galaxies have an exponential cut off around 100 keV. If all Seyfert galaxies and quasars have such spectra and undergo the same cosmological cvolution, one can explain the observed log N - log S relation of AGNs and the intensity and fluctuation of the XRB.