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High-Energy Gamma-Ray Observations of Active Galaxies

Published online by Cambridge University Press:  12 April 2016

Carl E. Fichtel
Carl E. Fichtel*
Affiliation:
NASA/Goddard Space Flight Center, Greenbelt, MD 20771

Abstract

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During the period from 1992 May to early 1992 November, the Energetic Gamma-Ray Experiment Telescope (EGRET) on board the Compton Gamma Ray Observatory obtained high-energy gamma-ray data for most of the sky. A total of 18 active galaxies have been seen with high certainty, and it is expected that more will be found in the data when a more thorough analysis is complete. All of those that have been seen are radio-loud quasars or BL Lacertae objects; most have already been identified as blazars. No Seyfert galaxies have been found thus far. If the spectra are represented as a power law in energy, spectral slopes ranging from approximately −1.7 to −2.4 are found. A wide range of z-values exists in the observed sample, eight having values in excess of 1.0. Time variations have been seen, with the timescale for a significant change being as short as days in at least one case. These results imply the existence of very large numbers of relativistic particles, probably close to the central object. Although a large extrapolation is required, their existence also suggests that these active galactic nuclei may be the source of the extragalactic cosmic rays.

Subject headings: acceleration of particles — galaxies: active — gamma rays: observations — quasars: general

Type
Active Galaxies and Quasi-Stellar Objects
Information
International Astronomical Union Colloquium , Volume 142: Particle Acceleration Phenomena in Astrophysical Plasmas , 1994 , pp. 917 - 922
Copyright
Copyright © The American Astronomical Society 1994

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