A tentative gamma-ray line from Dark Matter annihilation at the Fermi Large Area Telescope

Abstract

The observation of a gamma-ray line in the cosmic-ray fluxes would be a\nsmoking-gun signature for dark matter annihilation or decay in the Universe. We\npresent an improved search for such signatures in the data of the Fermi Large\nArea Telescope (LAT), concentrating on energies between 20 and 300 GeV. Besides\nupdating to 43 months of data, we use a new data-driven technique to select\noptimized target regions depending on the profile of the Galactic dark matter\nhalo. In regions close to the Galactic center, we find a 4.6 sigma indication\nfor a gamma-ray line at 130 GeV. When taking into account the look-elsewhere\neffect the significance of the observed excess is 3.2 sigma. If interpreted in\nterms of dark matter particles annihilating into a photon pair, the\nobservations imply a dark matter mass of 129.8\\pm2.4^{+7}_{-13} GeV and a\npartial annihilation cross-section of <\\sigma v> = 1.27\\pm0.32^{+0.18}_{-0.28}\nx 10^-27 cm^3 s^-1 when using the Einasto dark matter profile. The evidence for\nthe signal is based on about 50 photons; it will take a few years of additional\ndata to clarify its existence.\n