High Energy Emission from AGN and Unified Schemes

Abstract

Active Galactic Nuclei (AGN) are now known to be strong gamma-ray emitters. After briefly describing AGN classification and the main ideas behind unified schemes, I summarize the main properties of blazars (that is BL Lacs and flat-spectrum radio quasars) and their connection with relativistic beaming. Finally, I address the question of why blazars, despite being extreme and very rare objects, are the only AGN detected at high (E > 100 MeV) energies, and touch upon the relevance of TeV astronomy for AGN research.

12 pages, 2 figures. Invited talk at the Vulcano Workshop "Frontier Objects in Astrophysics and Particle Physics", to appear in the proceedings. Postscript file also available at http://icarus.stsci.edu/~padovani/unif_papers.html