Contribution from unresolved discrete sources to the extragalactic gamma-ray background (EGRB)

Bhattacharya, Debbijoy and Sreekumar, Parameswaran and Mukherjee, Reshmi (2009) Contribution from unresolved discrete sources to the extragalactic gamma-ray background (EGRB). In: Research in astronomy and astrophysics, 9 (11). pp. 1205-1214.

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Abstract

The origin of the extragalactic gamma-ray background (EGRB) is still an open question, even nearly forty years after its discovery. The emission could originate either from truly diffuse processes or from unresolved point sources. Although the majority of the 271 point sources detected by EGRET (Energetic Gamma Ray Experiment Telescope) are unidentified, of the identified sources, blazars are the dominant candidates. Therefore, unresolved blazars may be considered the main contributor to the EGRB, and many studies have been carried out to understand their distribution, evolution and contribution to the EGRB. Considering that gamma-ray emission comes mostly from jets of blazars and that the jet emission decreases rapidly with increasing jet to line-of-sight angle, it is not surprising that EGRET was not able to detect many large inclination angle active galactic nuclei (AGNs). Though Fermi could only detect a few large inclination angle AGNs during the first three months of its survey, it is expected to detect many such sources in the near future. Since non-blazar AGNs are expected to have higher density as compared to blazars, these could also contribute significantly to the EGRB. In this paper, we discuss contributions from unresolved discrete sources including normal galaxies, starburst galaxies, blazars and off-axis AGNs to the EGRB.

Item Type:	Journal Article
Publication:	Research in astronomy and astrophysics
Publisher:	Natl astronomical observatories, chin acad sciences
Additional Information:	copyright of this article belongs to Natl astronomical observatories, chin acad sciences.
Keywords:	galaxies:active;galaxies:jets;gamma-rays:observations.
Department/Centre:	Division of Physical & Mathematical Sciences > Physics
Date Deposited:	09 Jan 2010 08:03
Last Modified:	19 Sep 2010 05:53
URI:	http://eprints.iisc.ac.in/id/eprint/25299

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