We investigate contributions to the extragalactic gamma-ray background ( EGB ) due to neutralino dark matter ( DM ) pair-annihilation into photons , from DM density enhancements ( minispikes ) surrounding intermediate-mass black holes ( IMBHs ) .
We focus on two IMBH formation scenarios ; our conservative scenario where IMBHs are remnants of Population-III stars , and our optimistic scenario here IMBHs are formed in protogalactic disks .
In both scenarios , their formation in pregalactic halos at high redshift lead to the formation of minispikes that are bright sources of gamma-ray photons .
Taking into account minispike depletion processes , we only sum contributions from a cosmological distribution of IMBHs with maintained minispikes .
Our conservative scenario ( BH mass 10 ^ { 2 } M _ { \odot } with a r ^ { -3 / 2 } minispike ) predicts gamma-ray fluxes that are an order larger than the equivalent flux , using the same DM parameters ( mass 100 \mathrm { GeV } and annihilation cross-section 3 \times 10 ^ { -26 } \mathrm { cm ^ { 3 } s ^ { -1 } } ) , from the host halo without IMBH minispikes .
Our optimistic scenario ( BH mass 10 ^ { 5 } M _ { \odot } with a r ^ { -7 / 3 } minispike ) predicts fluxes that are three orders larger , that can reach current EGB observations taken by EGRET ( DM parameters as above ) .
This fact may serve interesting consequences for constraining DM parameters and elucidating the true nature of IMBHs .
Additionally , we determine the spectra of DM annihilation into monochromatic gamma-rays , and show that its flux can be within observational range of GLAST , providing a potential ‘ smoking-gun ’ signature of DM .