The dark connection between the EGRET excess of diffuse Galactic gamma rays, the Canis Major dwarf, the Monoceros ring, the INTEGRAL 511 keV annihilation line, the gas flaring and the Galactic rotation curve

TL;DR

The paper explores the possibility that the EGRET gamma ray excess is due to dark matter annihilation, supported by galactic substructures and consistent cosmic ray propagation models, challenging previous exclusion claims.

Contribution

It demonstrates that an anisotropic cosmic ray propagation model reconciles the gamma ray excess with antiproton flux data, supporting a dark matter annihilation interpretation.

Findings

Gamma ray excess compatible with dark matter annihilation in a standard halo profile.

Substructures at 4 and 13 kpc align with known galactic features and simulations.

Anisotropic propagation models fit gamma ray and cosmic ray data without excluding dark matter.

Abstract

The EGRET excess of diffuse Galactic gamma rays shows all the key features of dark matter annihilation (DMA) for a WIMP mass in the range 50-100 GeV, especially the distribution of the excess is compatible with a standard halo profile with some additional ringlike substructures at 4 and 13 kpc from the Galactic centre. These substructures coincide with the gravitational potential well expected from the ring of dust at 4 kpc and the tidal stream of dark matter from the Canis Major satellite galaxy at 13 kpc, as deduced from N-body simulations fitting to the Monoceros ring of stars. Strong independent support for this substructure is given by the gas flaring in our Galaxy. The gamma rays from DMA are originating predominantly from the hadronization of mono-energetic quarks, which should produce also a small, but known fraction of protons and antiprotons. Bergstrom et al. an antiproton flux far above the observed antiproton flux and they conclude that the DMA interpretation of the EGRET excess can therefore be excluded. However, they used an isotropic propagation model, i.e. the same diffusive propagation in the disk and the halo. It is shown that an anisotropic propagation model is consistent with the EGRET gamma ray excess, the antiproton flux and the ratios of secondary/primary and unstable/stable cosmic ray particles. Such an anisotropic propagation is supported by the large bulge/disk ratio of the positron annihilation line, as observed by the INTEGRAL satellite. In this case no need for new sources specific to the bulge are needed, so the claimed evidence for strong DMA in the bulge from these observations is strongly propagation model dependent.