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 (𝐸𝛾 >100  GeV) 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 ∼500  GeV and ∼25  TeV 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−2 s−1 sr−1 and (1 ×10−8–2 ×10−6)  m−2 s−1 sr−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 ⟨𝜎⁢𝑣⟩𝜒⁢𝜒→𝛾⁢𝛾 reach ∼10−27  cm3 s−1, based on the Einasto parametrization of the Galactic DM halo density profile.