Unification of AGN at hard X-rays
Résumé
Unified models of Active Galactic Nuclei (AGN) address the question whether or not the different types of AGN can be explained by the same intrinsic mechanism, altered only by external effects such as orientation to or absorption in the line of sight, or by the presence/absence of beamed emission. Hard X-ray spectra give the opportunity to investigate AGN in an energy range where absorption has little effect on the observed spectrum. Thus, in case different AGN types are intrinsically the same, their average hard X-ray spectra should be similar. Swift and INTEGRAL provide hard X-ray spectra of hundreds of AGN. Seyfert 1 and Seyfert 2 galaxies seem to show the same intrinsic spectra with photon index 1.9 and a reflection component of R=1. At the same time it appears that more luminous AGN are rather type 1 than of type 2 and that the unabsorbed sources dominate at high luminosities. A closer look at the brightest AGN, like Cen A and NGC 4151, adds more complications though. NGC 4151 data reveil a complex geometry, and the X-ray spectrum of Cen A leaves room for a non-thermal as well as for a thermal interpretation. We will discuss the current status of the unified model of AGN in view of the latest results on hard X-ray spectra and their connection to the gamma-rays as observed by Fermi/LAT and Cherenkov telescopes such as HESS, MAGIC, and VERITAS.