Active Galactic Nuclei: present observations and prospects
INTEGRAL has made a very significant contribution to our understanding of the physics of AGN. We illustrate this progress by looking at the considerations that were made at the time of the selection of the INTEGRAL mission and discussing some observations and results obtained in the intervening time. It is seen that while a number of results pertaining to the variability of AGN have been obtained, the potential of the INTEGRAL data in short timescale variability domain is still largely under exploited. The characteristic variability timescale of AGN, and X-ray binaries, can be understood in the frame of the cascade of shocks model and more generally depends solely on the Compton cooling properties of a hot electron plasma located at a distance proportional to the mass of the object from a soft photon source. Although INTEGRAL is not a focusing instrument, it is possible to resolve a small but significant fraction of the diffuse extragalactic background at energies higher than 10\,keV.