The EGRET excess of diffuse gamma rays and the galactic dark matter halo

Abstract

The public data from the EGRET space telescope on diffuse galactic gamma rays in the energy range from 0.1 to 10 GeV are reanalyzed with the purpose of searching for signals of dark matter annihilation (DMA). The analysis confirms the previously observed excess for energies above 1 GeV in comparison with the expectations from conventional galactic models. In addition, the excess was found to show all the key features of a signal from DMA: (a) the excess is observable in all sky directions and has the same shape everywhere, thus pointing to a common source; (b) the shape corresponds to the expected spectrum of the annihilation of non-relativistic massive particles (50–90 GeV) into neutral π₀ mesons, which decay into photons; (c) the excess traces the dark matter (DM) distribution in our galaxy, as proven by the reconstruction of the rotation curve from the intensity of the gamma ray excess.

These signals of DMA are compatible with supersymmetry for boost factors of 20 upwards and have a statistical significance of more than 10σ in comparison with the conventional galactic model. This statistical significance combined with the features mentioned above provides an intriguing hint that the EGRET excess is indeed a signal from DMA. Any conventional explanation of the gamma ray excess will not address the peculiar shape of the rotation curve above 11 kpc, which was attributed to the clustering of DM in a toroidal ringlike structure, presumably from the infall of a satellite galaxy.

Keywords:

• Halo
• Structure
• Rotation curve
• Dwarf galaxies
• Dark matter mass
• Baryonic mass
• Structure formation
• DMA
• Neutralinos
• Supersymmetry

Acknowledgements

I thank my close collaborators A. Gladyshev, D. Kazakov, C. Sander and V. Zhukov for their contributions to this exciting project. I thank V. Moskalenko, O. Reimers and A. Strong for sharing with us all their knowledge about our Galaxy and the EGRET data. This work was supported by the DLR (Deutsches Zentrum für Luft- und Raumfahrt).

Notes

NASA archive: http://cossc.gsfc.nasa.gov/archive/

The gravitational force is only zero in a spherical shell, not inside a ring.