Speaker
Description
The Fermi-LAT has confirmed and measured with unprecedent precision the extragalactic gamma-ray background (EGB), which is the sum of the flux of cataloged sources and the Isotropic diffuse gamma-ray background (IGRB). The IGRB is a highly-isotropic component on angular scales larger than 1 degree and whose composition is thought to be dominated by unresolved sources, i.e., sources that are not individually detected by the LAT.
We investigate the origin of the EGB using for the first time two complementary techniques: 1) a source-detection efficiency correction method and 2) an analysis of pixel photon count statistics with the 1-point probability distribution function (1pPDF). With the first method, using realistic Monte Carlo simulations of the gamma-ray sky, we calculate the efficiency of the LAT to detect point sources and this enables us to find the intrinsic source count distribution at photon fluxes. The source count distribution derived with this method is then compared to the one found with the 1pPDF method. The results obtained with these two methods are independent from extrapolation of fluxes below the sensitivity of the LAT and provide a precise estimation of the contribution of blazars to the Fermi EGB.
