Astrophysical explanations of suspected dark matter signals in dwarf galaxies

Abstract : We present methods to assess whether gamma-ray excesses towards Milky Way dwarf galaxies can be attributed to astrophysical sources rather than to dark matter annihilation. As a case study we focus on Reticulum II, the dwarf which shows the strongest evidence for a gamma-ray signal in Fermi data. Dark matter models and those with curved energy spectra provide good fits to the data, while a simple power law is ruled out at 97.5% confidence. We compare RetII's spectrum to known classes of gamma-ray sources and find a useful representation in terms of spectral curvature and the energy at which the spectral energy distribution peaks. In this space the blazar classes appear segregated from the confidence region occupied by RetII. Pulsars have similar gamma-ray spectra to RetII but we show that RetII is unlikely to host a pulsar population detectable in gamma rays. Tensions with astrophysical explanations are stronger when analyzing 6.5 years of Pass 7 than with the same amount of Pass 8 data, where the excess is less significant. These methods are applicable to any dwarf galaxy which is a promising dark matter target and shows signs of gamma-ray emission along its line of sight.
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Submitted on : Sunday, August 26, 2018 - 11:44:20 AM
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Alex Geringer-Sameth, Savvas M. Koushiappas, Matthew G. Walker, Vincent Bonnivard, Céline Combet, et al.. Astrophysical explanations of suspected dark matter signals in dwarf galaxies. 2018. ⟨hal-01861933⟩



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