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Title:
X-ray studies of active galactic nuclei
Authors:
Gandhi, P.
Affiliation:
AA(European Southern Observatory, Alonso de Cordova 3107, Casilla 19001, Santiago, Chile)
Publication:
Asian Journal of Physics, 13, p.90-107, Einstein centenary special edition book "Twenty First Century Astrophysics" - eds. Saha, S. K.; Rastogi, V. K., Anita Publications, 2005
Publication Date:
00/2005
Origin:
AUTHOR
Keywords:
galaxies: active, galaxies: X-rays, telescopes: X-rays
Bibliographic Code:
2005AsJPh..13...90G

Abstract

Super-massive black holes are ubiquitously found at the centres of large galaxies, and a sub-set of these are bright enough to outshine the entire galaxy that hosts each of them. These are called Active Galactic Nuclei (AGN), and they are engines transforming gravitational potential energy of accreting matter into radiation and outflows. Their tremendous radiative output spans the entire electromagnetic spectrum, but X-ray emission, in particular, provides information on processes occurring at their very cores. X-ray surveys have progressed significantly over the past decades and now provide an extremely effective strategy for locating AGN. This article focuses on observational X-ray studies of AGN from a phenomenological perspective. Our current understanding of AGN structure as derived from multi-wavelength studies is described, and the processes that generate observed AGN X-ray spectra are discussed. Key X-ray missions that advanced AGN studies are summarized. Finally, the cosmological relevance of AGN and several interesting discoveries from the latest X-ray surveys are discussed.
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