LogN–LogS Studies of EGRET Sources

A comprehensive investigation of logN–logS distributions of gamma-ray sources discovered by EGRET has been performed for subsequent use in population studies. Existing models explaining the spatial arrangement of unidentified sources do not compare against an observed logN–logS distribution. However, viable population models not only have to reproduce the logN–logS distribution for different source classes globally, they have to correspond to apparent differences among their spatial, spectral and variability characteristics. Furthermore, it needs to be understood in which way results from selections among the unidentified sources like ”persistent” (Grenier, 2000) or ”steady” sources (Gehrels et al., 2000) are related to the overall picture regarding their logN–logS characteristics.