Unresolved Unidentified Source Contribution to the Gamma-ray Background

TL;DR

This paper empirically estimates the significant contribution of unresolved unidentified gamma-ray sources to the extragalactic gamma-ray background and discusses how future observations can clarify their nature.

Contribution

It introduces an empirical method to assess the impact of unidentified sources on the gamma-ray background and explores how upcoming GLAST data can elucidate their origins.

Findings

Unresolved unidentified sources likely contribute significantly to the EGRB.

Upcoming GLAST observations can help identify the nature of these sources.

Method provides a way to analyze gamma-ray background without direct source identification.

Abstract

The large majority of EGRET point sources remain without an identified low-energy counterpart, and a large fraction of these sources are most likely extragalactic. Whatever the nature of the extragalactic EGRET unidentified sources, faint unresolved objects of the same class must have a contribution to the diffuse extragalactic gamma-ray background (EGRB). Understanding this component of the EGRB, along with other guaranteed contributions from known sources, is essential if we are to use this emission to constrain exotic high-energy physics. Here, we follow an empirical approach to estimate whether a potential contribution of unidentified sources to the EGRB is likely to be important, and we find that it is. Additionally, we show how upcoming GLAST observations of EGRET unidentified sources, as well as of their fainter counterparts, can be combined with GLAST observations of the Galactic and extragalactic diffuse backgrounds to shed light on the nature of the EGRET unidentified sources even without any positional association of such sources with low-energy counterparts.