Abstract
Recently, many studies indicate that the GeV gamma ray excess signal from the central Milky Way can be best explained by ∼40–50 GeV dark matter annihilating via the b b ¯ channel. However, this model appears to be disfavored by the recent Fermi-LAT data for dwarf spheroidal galaxies and the constraint from synchrotron radiation. In this article, we describe a consistent picture to relieve the tensions between the dark matter annihilation model and the observations. We show that a baryonic feedback process is the key to alleviate the tensions and the ∼40–50 GeV dark matter model is still the best one to account for the GeV gamma ray excess in the Milky Way.
Highlights
In the past few years, a considerable amount of excess GeV gamma rays emitted from our Galactic center were reported [1,2]
By considering the effect of baryonic feedback, we show that the most popular annihilation model (40–50 GeV dark matter annihilating via bb) basically satisfies the most stringent constraint, the synchrotron radiation constraint, even if a density spike exists near the supermassive black hole
Baryonic feedback can relieve the tensions among the adiabatic growth model of the supermassive black hole, the 40–50 GeV dark matter annihilation model, and the observational constraint of synchrotron radiation within 4”
Summary
In the past few years, a considerable amount of excess GeV gamma rays emitted from our Galactic center were reported [1,2]. By using the observed radio flux at 408 MHz emitted from a small region (r ≈ 0.16 pc) near the Galactic center [21], the largest annihilation cross section is constrained to < σv >∼ 10−27 cm s−1 for m = 50 GeV and γ = 1.26 [22], which is smaller than the best-fit annihilation cross section. If the supermassive black hole grows adiabatically from a smaller seed, the density spike would give a strong enhancement of the annihilation signal [23,24] If this is the case, the resulting upper limit based on radio observations would be much tighter. If the baryonic feedback process can remove the cusp structure of dark matter, ∼40–50 GeV dark matter annihilating via bbcan escape from all of the above constraints In other words, this dark matter annihilation model can still provide the best explanation of the GeV gamma ray excess in the Galactic center. This description can give a complete and better picture for the GeV gamma ray excess problem
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