The intrinsic emission of Seyfert galaxies observed with BeppoSAX/PDS - I. Comparison of the average spectra of the three classes of Seyfert galaxies

We present a study of the hard X-ray spectrum (>15 keV) of different classes of Seyfert galaxies observed with BeppoSAX/PDS. Using hard X-ray data, we avoid absorption effects modifying the Seyfert emission and have direct access to the central engine of these sources. The aim of this study is first to characterize the general properties of the hard X-ray spectrum of Seyfert 1, 1.5 and 2 galaxies and secondly to compare their intrinsic emission to test unified models according to which all the classes have the same nucleus. We compute the average spectrum of 14 Sy 1, 9 Sy 1.5 and 22 Sy 2 galaxies observed by the PDS (15-136 keV). The average spectrum of Sy 1 differs from that of Sy 2, the first requiring the presence of a high energy cutoff which is absent in the second. We also show that the reflection component is possibly more important in the Sy 2 emission. The nature of Sy 1.5 galaxies is ambiguous as they have a negligible reflection component (like Sy 1) and do not require a cutoff (like Sy 2).