Possible Evidence For Dark Matter Annihilation In The Inner Milky Way From The Fermi Gamma Ray Space Telescope

Abstract

We study the gamma rays observed by the Fermi Gamma Ray Space Telescope from the direction of the Galactic Center and find that their angular distribution and energy spectrum are well described by a dark matter annihilation scenario. In particular, we find a good fit to the data for dark matter particles with a 25-30 GeV mass, an annihilation cross section of ~9x10^-26 cm^3/s, and that are distributed with a cusped halo profile within the inner kiloparsec of the Galaxy. We cannot, however, exclude the possibility that these photons originate from an astrophysical source or sources with a similar morphology and spectral shape to those predicted in an annihilating dark matter scenario.

Figures (2)

• Figure 1: The angular distribution of gamma rays around the Galactic Center observed by the FGST. In each frame, the dashed line denotes the shape predicted for the annihilation products of dark matter distributed according to a halo profile which is slightly cuspier than NFW ($\gamma=1.1$). The dotted line is the prediction from the previously discovered TeV point source located at the Milky Way's dynamical center, while the dot-dashed line denotes the diffuse background described in the text (which, although included in each case, falls below the range of rates shown in the upper four frames). The solid line is the sum of these contributions.
• Figure 2: The gamma ray spectrum measured by the FGST within 0.5$^{\circ}$ (left) and 3$^{\circ}$ (right) of the Milky Way's dynamical center. In each frame, the dashed line denotes the predicted spectrum from a 28 GeV dark matter particle annihilating to $b\bar{b}$ with a cross section of $\sigma v = 9\times 10^{-26}$ cm$^3$/s, and distributed according to a halo profile slightly more cusped than NFW ($\gamma=1.1$). The dotted and dot-dashed lines denote the contributions from the previously discovered TeV point source located at the Milky Way's dynamical center and the diffuse background, respectively. The solid line is the sum of these contributions.