Gamma-ray Emitting AGN and Unified Schemes


Paolo Padovani

Original Version: `Very High Energy Phenomena in the Universe', Y. Giraud-Heraud and J. Tran Thanh Van eds., Editions Frontieres, p. 7.

(Invited Review Talk at the XXXIInd Moriond Conference , Les Arcs, January 1997)

Text copyright (c) 1997: Editions Frontieres

Abstract

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

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