Extracting limits on Dark Matter annihilation from gamma-ray observations towards dwarf spheroidal galaxies

Abstract

Dwarf spheroidal galaxies compose one of the most dark matter dominated classes of objects, making them a set of targets to search for signals of dark matter annihilation. Recent developments in gamma-ray astronomy, most importantly the launch of the Fermi-LAT instrument, have brought those targets into attention. Yet, no clear excess of gamma-rays has been confirmed from these targets, resulting in some of the tightest limits on dark matter annihilation from indirect searches. In extracting limits from dwarf spheroidal galaxies, it is of great importance, to properly take into account all relevant uncertainties. Those include the dark matter distribution properties of the dwarf spheroidals and the uncertainties on the underlying background. We revisit the limits on dark matter annihilation, from gamma-rays studying a set of close-by dwarf spheroidal galaxies, for which, we have good understanding of the uncertainties in the dark matter distribution. For those targets, we perform and compare results for alternative methods in extracting the background gamma-ray flux. This provides a method to discriminate among the dark matter annihilation targets, those that can give robust constraints. We finally present our tightest limits on dark matter annihilation, that come only from the targets that ensure accurate understanding of both the gamma-ray background and the dark matter distribution uncertainties.

22 pages, 12 figures, 4 tables, slight change of title. v2 agrees with the published PRD version

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• A Tentative Gamma-Ray Line from Dark Matter Annihilation at the Fermi Large Area Telescope