Galactic Center radio constraints on gamma-ray lines from dark matter annihilation

Abstract

Recent evidence for one or more gamma-ray lines at $\ensuremath{\sim}130\text{ }\text{ }\mathrm{GeV}$ in the Fermi-LAT data from the Galactic Center has been interpreted as a hint for dark matter annihilation to $Z\ensuremath{\gamma}$ or $H\ensuremath{\gamma}$ with an annihilation cross section of $⟨\ensuremath{\sigma}v⟩\ensuremath{\sim}{10}^{\ensuremath{-}27}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$. We test this hypothesis by comparing synchrotron fluxes due to the electrons and positrons from decay of the $Z$ or the $H$ bosons only against radio data from the same region in the Galactic Center. We find that the radio data from single-dish telescopes marginally constrain this interpretation of the claimed gamma lines for a contracted NFW profile. Already-operational radio telescopes, such as Long Wavelength Array, VLA-Low, and Low-Frequency Array for Radio Astronomy, and future radio telescopes like SKA, are sensitive to annihilation cross sections of the order of ${10}^{\ensuremath{-}28}\text{ }\text{ }{\mathrm{cm}}^{3}\text{ }{\mathrm{s}}^{\ensuremath{-}1}$ and can confirm or rule out this scenario very soon. We discuss the dependencies on the dark matter profile, magnetic fields, and background radiation density profiles, and show that the constraints are relatively robust for any reasonable assumptions. Independent of the above said recent developments, we emphasize that our radio constraints apply to all models where dark matter annihilates to $Z\ensuremath{\gamma}$ or $H\ensuremath{\gamma}$.