Fermi Gamma-ray Space Telescope

A background-model-independent analysis of the Fermi Large Area Telescope gamma-ray data from the Milky Way dwarf galaxies to constrain dark matter scenarios

M. N. Mazziotta
L. Di Venere, F. Loparco

Abstract:

The dwarf spheroidal satellite galaxies (dSphs) of the Milky Way are a promising target for indirect dark matter searches with gamma rays because of their large dark matter content and the low astrophysical foregrounds. Here we present a background-model-independent technique to perform the data analysis of a sample of dSphs observed by the Large Area Telescope (LAT) onboard the Fermi satellite. This is a complementary approach to the standard Fermi-LAT point-source analysis, as implemented in the Science Tools, and is based on the analysis of the photon count spectra detected in a signal region and in a control region. The first is a circle centered on the nominal position of the source, while the latter is an annulus centered on the source position, external to the signal region, with the exclusion of all known sources. The approach is background-model-independent since it does not require any assumption on the diffuse and the isotropic backgrounds. First we search for a possible evidence of a signal, then we constrain the dark matter pair annihilation cross section for several standard model channels in the WIMP scenario. The results are obtained applying a Bayesian analysis to the recent public Pass 8 LAT data. A comparison of our results is shown with those obtained with a modeling of the background counts evaluated after fitting the diffuse background templates.