GeV Gamma-ray Excess Research Articles

Updated cosmic-ray and radio constraints on light dark matter: Implications for the GeV gamma-ray excess at the Galactic Center

The apparent gamma-ray excess in the Galactic center region and inner Galaxy has attracted considerable interest, notably because both its spectrum and its radial distribution are consistent with an interpretation in terms of annihilating dark matter particles with a mass of about 10--40 GeV. We confront such an interpretation with an updated compilation of various indirect dark matter detection bounds, which we adapt to the specific form required by the observed signal. We find that cosmic-ray positron data strongly rule out dark matter annihilating to light leptons, or ``democratically'' to all leptons, as an explanation of the signal. Cosmic-ray antiprotons, for which we present independent and significantly improved limits with respect to previous estimates, are already in considerable tension with dark matter (DM) annihilation to any combination of quark final states; the first set of AMS-02 data will thus be able to rule out or confirm the DM hypothesis with high confidence. For reasonable assumptions about the magnetic field in the Galactic center region, radio observations independently put very severe constraints on a DM interpretation of the excess, in particular for all leptonic annihilation channels.

Fermi-LAT gamma-ray signal from Earth limb, systematic detector effects and their implications for the 130 GeV gamma-ray excess

We look for possible spectral features and systematic effects in Fermi-LAT publicly available high-energy gamma-ray data by studying photons from the Galactic centre, nearby galaxy clusters, nearby brightest galaxies, AGNs, unassociated sources, hydrogen clouds and Earth Limb. Apart from already known 130 GeV gamma-ray excesses from the first two sources, we find no new statistically significant signal from others. Much of our effort goes to studying Earth Limb photons. In the energy range 30 GeV to 200 GeV the Earth Limb gamma-ray spectrum follows power-law with spectral index 2.87\pm 0.04 at 95 % CL, in a good agreement with the PAMELA measurement of cosmic ray proton spectral index between 2.82-2.85, confirming the physical origin of the Limb gamma-rays. In small subsets of Earth Limb data with small photon incidence angle it is possible to obtain spectral features at different energies, including at 130 GeV, but determination of background, thus their significances, has large uncertainties in those cases. We observe systematic 2\sigma level differences in the Earth Limb spectra of gamma-rays with small and large incidence angles. The behaviour of those spectral features as well as background indicates that they are likely statistical fluctuations.

Fermi 130 GeV gamma-ray excess and dark matter annihilation in sub-haloes and in the Galactic centre

We analyze publicly available Fermi-LAT high-energy gamma-ray data and confirm the existence of clear spectral feature peaked at Eγ = 130 GeV. Scanning over the Galaxy we identify several disconnected regions where the observed excess originates from. Our best optimized fit is obtained for the central region of Galaxy with a clear peak at 130 GeV with local statistical significance 4.5σ. The observed excess is not correlated with Fermi bubbles. We compute the photon spectra induced by dark matter annihilations into two and four standard model particles, the latter via two light intermediate states, and fit the spectra with data. Since our fits indicate sharper and higher signal peak than in the previous works, data favors dark matter direct two-body annihilation channels into photons or other channels giving only line-like spectra. If Einasto halo profile correctly predicts the central cusp of Galaxy, dark matter annihilation cross-section to two photons is of order ten percent of the standard thermal freeze-out cross-section. The large dark matter two-body annihilation cross-section to photons may signal a new resonance that should be searched for at the CERN LHC experiments.