Variability of EGRET Gamma‐Ray Sources

The variability of the high-energy gamma ray sources in the Third EGRETcatalog is analyzed by a new method. We re-analyze the EGRET data to calculatea likelihood function for the flux of each source in each observation, both fordetections and upper limits. These functions can be combined in a uniformmanner with a simple model of the flux distribution to characterize the fluxvariation by a confidence interval for the relative standard deviation of theflux. The main result is a table of these values for almost all the catalogedsources. As expected, the identified pulsars are steady emitters and theblazars are mostly highly variable. The unidentified sources are heterogeneous,with greater variation at higher Galactic latitude. There is an indication thatpulsar wind nebulae are associated with variable sources. There is a populationof variable sources along the Galactic plane, concentrated in the inner spiralarms.