INTEGRAL and the unified model of AGN

Abstract

According to the unified model, the differences observed in different classes of AGN are due to anisotropic obscuration. This implies that in the hard X-rays, at energies where the radiation can pierce the obscuring material, the average spectral characteristics of different classes of AGN should be the same. Here we present a study of the 17-250 keV INTEGRAL IBIS/ISGRI average spectra of Seyfert galaxies, aimed to constrain similarities and possible differences between different classes of AGN. The sample we consists of all the 172 Seyfert galaxies detected by INTEGRAL IBIS/ISGRI at z<0.2 during its first 7 years of observations. Of these, 45 are Seyfert 1s, 31 Seyfert 1.5s, 67 Compton-thin Seyfert 2s, 11 Narrow Line Seyfert 1s, 11 Compton-thick Seyfert 2s, and 9 LINERs. Comparing the average hard X-ray spectra of the different classes we found that, while the spectra of Seyfert 1s, Seyfert 1.5 and NLS1s are consistent, Compton-thin Seyfert 2 show a clear excess in the 20-60 keV band over the spectrum of Seyfert 1s and Seyfert 1.5s. This excess might be due to an intrinsically stronger reflection component or to a clumpy structure of the absorber in Compton-thin Seyfert 2s.