EGRET excess of diffuse galactic gamma rays interpreted as a signal of dark matter annihilation.

Elsaesser and Mannheim [1] fit a contribution of Dark Matter Annihilation (DMA) to the extragalactic contribution of the galactic diffuse gamma ray flux, as deduced from the EGRET data by Strong, Moskalenko and Reimer [2]. FIG. 1: The extragalactic flux of diffuse gamma rays compared with a simple power low (thick (black) line) and the sum of a steeply falling background plus a WIMP annihilation signal (grey (red) line with the components as dashed lines). They find a WIMP mass of 515 +110 −75 GeV and quote a systematic error of 30%. However, they do not include large systematic uncertainties from the fact that the determination of the extragalactic flux (EGF) requires a model for the subtraction of the Galactic flux from the data. The data used were obtained with a model without Galactic DMA, so one expects additional uncertainty in the region where DMA contributes. This is demonstrated in Fig. 1, where the EGF is obtained by subtracting the Galactic contribution including the contribution from DMA [3]. The latter was determined from the excess of the EGRET data above the background from nuclear interactions in all sky directions, which allows to obtain a parametrization of the halo profile. This halo profile was shown to describe the peculiar shape of the rotation curve of our Galaxy [4], thus proving that the Galactic excess of EGRET data traces the DM. With this DM halo profile the total Galactic flux including DMA can be calculated in all directions and subtracted from the EGRET data using the pioneering method of Sreekumar et al. [5]. This procedure was repeated for 8 different energy bins and the results are plotted in Fig.1. As expected , the high energy tail differs considerably from Ref. [2] and can be either fitted with a simple power law, which yields a χ 2 /d.o.f of 10.9/6 or a probability of 9%, or by a double power law plus a contribution from DMA with a WIMP mass of 50 GeV, which yields a χ 2 /d.o.f of 4.7/4 or a probability of 31%. For the latter fit the shape of DMA was taken from Ref. [4] and the shape of the remaining contribution of the EGF could be fitted with a double power law, typical of many point sources. Both probabilities are acceptable, so there is no evidence for a signal of DMA in the extragalactic flux, but on the …