Intermediate Mass Black Holes and Nearby Dark Matter Point Sources: A Critical Reassessment

Dark matter (DM) “minispikes” around intermediate mass black holes are sometimes quoted as one of the most promising targets for indirect DM searches. Here, we stress that existing cosmic ray data place severe constraints on the possibility to detect DM annihilation signals from these objects in gamma rays; observational prospects for neutrinos or charged cosmic rays seem even worse. Similar bounds severely constrain the possibility that the excess in the cosmic ray positron or electron flux recently reported by PAMELA/ATIC could be due to a nearby point source like a DM clump or minispike.

Figure 1

The thin solid lines show the constraints on WIMPs in the IMBH scenario B of 2, from top to bottom deriving from the brightest 10, 4, and 1 object(s), respectively. The region above the thick solid line is excluded by the EGRET limit on unresolved point sources; the dotted lines show the corresponding constraint if DM were to annihilate only into $e^{+}{e}^{-}$ or ${\mu }^{+}{\mu }^{-}$. The dashed line indicates the canonical value of $\sigma v=3\times {10}^{-26}{\mathrm{cm}}^3{\mathrm{s}}^{-1}$ for thermally generated WIMPs.

Figure 2

The solid lines give the EGRET constraints on the DM annihilation rate $\Gamma =\frac{1}{2}\sigma v({\rho }_0/m_{\chi }{)}^2\xi$ of a nearby, generic DM point source at a distance $d$ from the Earth; from left to right, we show the case of KK DM and a fiducial DM candidate annihilating to $e^{+}{e}^{-}$ and ${\mu }^{+}{\mu }^{-}$, respectively. The dashed lines show the $\Gamma$ needed to fit the PAMELA data, for sets of propagation parameters as defined in 23; in the dark shaded area this would produce an $e^{\pm }$ flux in conflict with the Fermi data at higher energies. For comparison, the dotted line indicates $\Gamma$ for the whole Milky Way, assuming $⟨\sigma v⟩\sim 3\times {10}^{-26}{\mathrm{cm}}^{-3}{\mathrm{s}}^{-1}$.