Robust Identification of Isotropic Diffuse Gamma Rays from Galactic Dark Matter

Dark matter annihilation in Galactic substructure will produce diffuse gamma-ray emission of remarkably constant intensity across the sky, making it difficult to disentangle this Galactic dark matter signal from the extragalactic gamma-ray background. We show that if Galactic dark matter contributes a modest fraction of the measured emission in an energy range accessible to the Fermi Gamma-ray Space Telescope, the energy dependence of the angular power spectrum of the total measured emission could be used to confidently identify gamma rays from Galactic dark matter substructure.

Figure 1

Top panel: Example measured isotropic diffuse intensity spectrum. Shown individually are the spectra of Galactic dark matter substructure for $m_{\chi }=700\mathrm{GeV}$, the reference blazar model without and with EBL attenuation ($z_0=0.4$), and the unattenuated alternative blazar model. The “total” signal is the sum of the attenuated reference blazar spectrum and the dark matter spectrum. The EGRET measurement of the EGRB is plotted for reference (black crosses). Bottom panel: Energy dependence of the angular power spectrum of the total isotropic emission at multipole $\ell =100$ for the scenario shown in the top panel. The anisotropy energy spectrum of Galactic dark matter substructure, unresolved blazars, and the total signal are shown.

Figure 2

Same as Fig. 1, for $m_{\chi }=80\mathrm{GeV}$. For the attenuated reference blazar model, $z_0=1$.