Unidentified EGRET Sources and the Extragalactic Gamma-Ray Background

The large majority of EGRET point sources remain to this day without an identified low-energy counterpart. But whatever the nature of these sources, we can be certain of one thing: faint unresolved objects of the same class must have a contribution to the diffuse gamma-ray emission.

If most unidentified sources 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 enhance the unresolved emission from their hosts. Unless we understand this component of the gamma-ray background, along with other guaranteed contributions from known sources, we cannot effectively 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 show how the GLAST measurement of the diffuse gamma-ray background will help us determine the location and effect of the majority of the EGRET unidentified sources.

Reference: Pavlidou, V., Siegal-Gaskins, J.M., Brown, C., Fields, B. D., & Olinto, A.V. 2006, to appear in APSS
Get the paper