The unified Seyfert scheme and the origin of the cosmic X-ray background

We discuss a simple model for the cosmic X-ray background (XRB), based on the unified Seyfert scheme. We show that a mixture of unabsorbed type 1 and absorbed type 2 Seyferts, integrated in redshift back to z = 3.5, can simultaneously reproduce the spectrum of the XRB from 1 to 150 keV and the source counts in both the soft and hard X-ray bands. The presence of numerous, heavily obscured sources with hard spectra at a flux level of 10 –12 erg cm –2 s –1 is indicated as a test of the model, in view of forthcoming ASCA observations.