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Astron. Astrophys. 344, 744-748 (1999)

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Testing the origin of the extragalactic gamma ray background by modelling its high energy spectrum

B. Weferling 1 and R. Schlickeiser 2

1 Max-Planck-Institut für Radioastronomie Bonn, Postfach 2024, D-53010 Bonn, Germany (weferlin@mpifr-bonn.mpg.de)
2 Institut für Theoretische Physik, Lehrstuhl IV, Ruhr-Universität Bochum, Postfach 102148, D-44721 Bochum, Germany (rsch@egal.tp4.ruhr-uni-bochum.de)

Received 9 June 1998 / Accepted 3 November 1998


The origin of the Extragalactic Gamma Ray Background (EGRB) is still a matter of discussion. With the increasing number of detected gamma ray point sources, it becomes increasingly likely that the seemingly diffuse EGRB is a superposition of the radiation of still unresolved point sources. Most models describe the gamma radiation of these point sources in accordance with the Unified Scheme (US) of Active Galactic Nuclei (AGN) as generated through a process of inverse Compton scattering in relativistically beamed plasma blobs in blazars. Earlier theoretical calculations of the contribution of these point sources to the EGRB have failed to consider the anisotropic beaming characteristics of the blazars. We show that it is possible to model the EGRB on the basis of the assumption that it is generated by unresolved blazars when these anisotropic effects are properly taken into account. Furthermore we demonstrate, using the example of an idealised blazar model, that predictions of the EGRB-spectrum at high energies can be made, which can in principle be used to test whether the EGRB is generated by unresolved blazars. We argue that the principle of that test applies not only to blazars, but also to every possible point source with anisotropic beaming pattern.

Key words: galaxies: active – cosmology: diffuse radiation – gamma rays: theory

Send offprint requests to: B. Weferling

© European Southern Observatory (ESO) 1999

Online publication: March 29, 1999