Supersymmetric Dark Matter and the Extragalactic Gamma Ray Background

We trace the origin of the newly determined extragalactic gamma-ray background from EGRET data to an unresolved population of blazars and neutralino annihilation in cold dark matter halos. Using results of high-resolution simulations of cosmic structure formation, we calculate composite spectra and compare with the EGRET data. The resulting best-fit value for the neutralino mass is $m_{\chi }={515}_{-75}^{+110}\mathrm{GeV}$ (systematic errors $\sim 30\%$).

Figure 1

(a) Results of the ${\chi }^2$ test of the neutralino annihilation hypothesis against the measured EGB. The annihilation cross section times $\Psi$ is normalized to the NFW-profile case [$\Gamma (0)=2\times {10}^6$] (b) Scatter plot of MSSM neutralinos created by scanning the parameter space described in Table ; the rectangle denotes the 520 GeV neutralino further explored in Fig. 2.

Figure 2

Extragalactic gamma-ray background: spectrum as determined from EGRET data by Strong et al. (data points) [the upper limit in the (60–100) GeV range is from Sreekumar et al.], steep power-law component (dashed line), straw person’s blazar model (dotted line), neutralino annihilation spectrum (orange solid line), and combined steep power law plus annihilation spectrum (red solid line).