Low-latitude gamma-ray sources: correlations and variability

Abstract

A review of the main characteristics of low-latitude sources in the third EGRET catalog is presented. There are 75 unidentified gamma-ray sources detected by EGRET at less than 10 degrees from the galactic plane. About a half of these sources are spatially correlated with potential galactic gamma-ray emitters such as supernova remnants, OB associations and early-type stars with very strong stellar winds. The other half is formed by sources without positional correlation with known galactic objects capable to generate a gamma ray flux significant enough as to be detected by EGRET. A variability analysis shows that this second group of sources contains several objects with high levels of gamma-ray variability. These variable sources resemble very much the AGNs detected by EGRET, but without their typical strong radio emission. To establish the nature of these sources is one of the most urgent problems of high-energy astrophysics.