Unidentified EGRET sources and the extragalactic gamma-ray background

Vasiliki Pavlidou, Jennifer M. Siegal-Gaskins, Carolyn Brown, Brian D. Fields, Angela V. Olinto

Research output: Contribution to journalArticlepeer-review


The large majority of EGRET point sources remain to this day without an identified low-energy counterpart. Whatever the nature of the EGRET unidentified sources, faint unresolved objects of the same class must have a contribution to the diffuse gamma-ray background: if most unidentified objects are extragalactic, faint unresolved sources of the same class contribute to the background, as a distinct extragalactic population; on the other hand, if most unidentified sources are Galactic, their counterparts in external galaxies will contribute to the unresolved emission from these systems. Understanding this component of the gamma-ray background, along with other guaranteed contributions from known sources, is essential in any attempt to use gamma-ray observations to constrain exotic high-energy physics. Here, we follow an empirical approach to estimate whether a potential contribution of unidentified sources to the extragalactic gamma-ray background is likely to be important, and we find that it is. Additionally, we comment on how the anticipated GLAST measurement of the diffuse gamma-ray background will change, depending on the nature of the majority of these sources.

Original languageEnglish (US)
Pages (from-to)81-87
Number of pages7
JournalAstrophysics and Space Science
Issue number1-4
StatePublished - Jun 2007


  • Gamma rays: observations
  • Gamma-ray sources: astronomical
  • Radiation sources: unidentified

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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