Ruling Out Spiky WIMP Dark Matter using Indirect Searches

Abstract

The dark matter (DM) density profile in the innermost region of the Galaxy remains an open question. In particular, while adiabatic growth of the supermassive black hole Sgr A$^\ast$ at the Galactic Center (GC) can induce a 'spike' in central DM density, the existence of such a spike is still under debate. Here we present new constraints on the spike slope $\gamma_{\rm sp}$ using conventional DM indirect detection searches. We first recast existing photon and neutrino line searches, which include the contribution from the GC region, into constraints on the thermally-averaged DM annihilation cross section $\langle\sigma v\rangle$ in the presence of a DM spike. We then derive new bounds on the spike profile for a generic Weakly Interacting Massive Particle (WIMP) DM scenario, where the thermal freeze-out mechanism fixes the annihilation cross-section at $\langle\sigma v\rangle\sim (2-3) \times 10^{-26}~{\rm cm}^3~{\rm s}^{-1}$. We find that, for DM annihilation to photons, existing \emph{Fermi}-LAT and MAGIC data place strong constraints on spike profiles at the GC over a broad range of WIMP DM masses, from 10 GeV to 100 TeV, for photon branching fractions down to $\sim 10^{-2}$, and remain sensitive to values as small as $\sim 10^{-4}$ in parts of the parameter space. For the neutrino channel, we use the recent IceCube data to constrain the existence of an extremely steep spike in the $\mathscr{O}(1-10)$~TeV DM mass range. Our analysis can be easily extended to other annihilation channels.