Searching for Gamma Rays from Galaxy Clusters with the Fermi Large Area Telescope Cosmic Rays and Dark Matter

Abstract: In this licentiate thesis, I report a search for GeV ? rays towards the location of Galaxy clusters. I mainly discuss the results of a search for cosmic-ray (CR) induced ?-ray emission but also briefly elaborate on a related study, searching for Dark Matter (DM)-induced ?-ray emission from Galaxy clusters. In addition, I provide a detailed discussion on the analysis tools that were used and discuss some additional tests that are not included in the papers this licentiate thesis is based on.In a comprehensive search almost covering the entire sky, we find no statistically significant evidence for either DM or CR induced ? rays from galaxy clusters. Thus we report upper limits on CR quantities that exclude emission scenarios in which the maximum hadronic injection efficiency is larger than 21% and associated limits on the maximum CR-to-thermal pressure ratio, <XCR>. In addition, we update previous flux upper limits given a new set of modeling and taking the source extension into account. For a DM masses below 100 GeV, we exclude annihilation cross sections above ? 10?24 cm3 s?1 into bb. For decaying DM, we exclude decay times lower than 1027 s over the mass range of 20 GeV– 2 TeV.