Abstract
Gamma-ray line signatures can be expected in the very-high-energy (E(γ)>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 ⟨σv⟩(χχ → γγ) reach ∼ 10(-27) cm(3)s(-1), based on the Einasto parametrization of the Galactic DM halo density profile.
Highlights
In the last few years, imaging atmospheric Cherenkov telescopes (IACTs) have been used to search for dark matter (DM) signals in very-high-energy (VHE; Eγ > 100 GeV) γ rays [1–10]
a search for spectral γ-ray signatures at very-high energies was performed based on H.E.S.S. observations of the central Milky Way halo region
Upper limits on monochromatic γ-ray line signatures were determined for the first time for energies
Summary
In the last few years, imaging atmospheric Cherenkov telescopes (IACTs) have been used to search for dark matter (DM) signals in very-high-energy (VHE; Eγ > 100 GeV) γ rays [1–10]. Objects with large predicted DM density, like the Galactic centre (GC), the central Galactic halo region (CGH), dwarf galaxies or centres of nearby galaxies were studied All such searches concentrated on the detection of γ rays produced in decays of secondary particles – mostly neutral mesons – in the process of DM self-annihilation or decay The second region is the extragalactic sky covered by H.E.S.S. observations, with regions containing known VHE γ-ray sources being excluded from the analysis For both data sets, the uncertainty on the strength of a putative DM annihilation signal is much reduced in comparison to the observations of centres of galaxies: for the CGH, the very centre is not considered, avoiding a region where the DM profile is only poorly constrained [8]. That a potentially large (but highly uncertain) γ-ray flux from Galactic DM annihilations may contribute to the extragalactic analysis [20]
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