Search for Photon-Linelike Signatures from Dark Matter Annihilations with H.E.S.S.

Gamma-ray line signatures can be expected in the very-high-energy (E_γ>100GeV) domain due to self-annihilation or decay of dark matter (DM) particles in space. Such a signal would be readily distinguishable from astrophysical γ-ray sources that in most cases produce continuous spectra that span over several orders of magnitude in energy. Using data collected with the H.E.S.S. γ-ray instrument, upper limits on linelike emission are obtained in the energy range between ∼500GeV and ∼25TeV for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. No statistically significant signal could be found. For monochromatic γ-ray line emission, flux limits of (2×10^-7-2×10^-5)m^-2s^-1sr^-1 and (1×10^-8-2×10^-6)m^-2s^-1sr^-1 are obtained for the central part of the Milky Way halo and extragalactic observations, respectively. For a DM particle mass of 1 TeV, limits on the velocity-averaged DM annihilation cross section ⟨σv⟩_χχ→γγ reach ∼10^-27cm³s^-1, based on the Einasto parametrization of the Galactic DM halo density profile.