Origin of the gamma rays from the Galactic Center

Abstract

The region surrounding the center of the Milky Way is both astrophysically rich and complex, and is predicted to contain very high densities of dark matter. Utilizing three years of data from the Fermi Gamma Ray Space Telescope (and the recently available Pass 7 ultraclean event class), we study the morphology and spectrum of the gamma ray emission from this region and find evidence of a spatially extended component which peaks at energies between 300 MeV and 10 GeV. We compare our results to those reported by other groups and find good agreement. The extended emission could potentially originate from either the annihilations of dark matter particles in the inner galaxy, or from the collisions of high energy protons that are accelerated by the Milky Way's supermassive black hole with gas. If interpreted as dark matter annihilation products, the emission spectrum favors dark matter particles with a mass in the range of 7-12 GeV (if annihilating dominantly to leptons) or 25-45 GeV (if annihilating dominantly to hadronic final states). The intensity of the emission corresponds to a dark matter annihilation cross section consistent with that required to generate the observed cosmological abundance in the early universe (σv ∼ 3 × 10 −26 cm 3 /s). We also present conservative limits on the dark matter annihilation cross section which are at least as stringent as those derived from other observations. PACS numbers: 95.85.Pw,95.55.Ka,95.35.+d; FERMILAB-PUB-11-505-A arXiv:1110.0006v1 [astro-ph.HE]

Anisotropy of the extragalactic radio background from dark matter annihilation

“…This has the effect of decreasing the necessary electron production rate and decreasing the anisotropy in high frequency observations, as shown in Section II. Second, these models are well motivated by their ability to explain the γ-ray signal observed in the Galactic Center by the Fermi-LAT telescope [11][12][13][14][15][16][17][18][19][20][21].…”

“…3, but for Case C as described in Sec V. Specifically, the dark matter is assumed to have a mass of 8 GeV and annihilate democratically to leptonic final states (33% to e + e − , 33% to µ + µ − and 33% τ + τ − ) [13,66,67]. In addition, the dark matter is assumed to follow a NFW profile, but the electrons from the annihilation are assumed to undergo reacceleration in the Alfvén waves powered by the cluster mergers [73,74].…”

“…In this case we find that the spectrum of the radio emission fits observations well up to a frequency of ∼4 GHz, when it begins to fall below the best fit observations. We note that the statistical fit to the ARCADE-2 data is still poor, Table I, where the dark matter is assumed to have a mass of 8 GeV and annihilate democratically to leptonic final states (33% to e + e − , 33% to µ + µ − and 33% τ + τ − ) [13,66,67]. In this case, the dark matter substructure is required to extend only to r sub = 4 rvir and the lower limit on the magnetic field is only B * sub = 4 µG.…”

“…Subsequent investigations determined that the emission intensity and spectrum resulting from the annihilation of relatively low mass (m χ < ∼ 100 GeV) dark matter provided a reasonable fit to the ARCADE-2 excess. These classes of models are additionally motivated as an explanation to the γ-ray excess observed near the galactic center of the Milky Way [11][12][13][14][15][16][17][18][19][20][21].…”

Multi-frequency search for Dark Matter: the role of HESS, CTA, and SKA

“…However, despite the character of DM proving elusive, γ-ray telescope projects like Fermi-LAT [1] and HESS [2, 3,4] continue to be effective in probing the parameter space of DM composed of Weakly Interacting Massive Particles (WIMPs) [5,6,7]. Of the two aforementioned projects, HESS has devoted far less time to this search as its sensitivity interval is largely unsuited to the study of the kind of low mass WIMPs that might be consistent with the excess γ-rays from the galactic centre, as well as the PAMELA [8] and AMS anti-particle experiments [9,10,11,12]. However, both HESS and the upcoming Cherenkov Telescope Array (CTA) [13,4] are admirably suited to probe large mass WIMPs.…”