Search for Dark Matter Annihilations towards the Inner Galactic Halo from 10 Years of Observations with H.E.S.S.

The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using 𝛾-ray observations towards the inner 300 pc of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10 years (2004–2014), and does not show any significant 𝛾-ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section ⟨𝜎⁢𝑣⟩. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach ⟨𝜎⁢𝑣⟩ values of 6×10⁻²⁶  cm³ s⁻¹ in the 𝑊+⁢𝑊− channel for a DM particle mass of 1.5 TeV, and 2×10⁻²⁶  cm³ s⁻¹ in the 𝜏+⁢𝜏− channel for a 1 TeV mass. For the first time, ground-based 𝛾-ray observations have reached sufficient sensitivity to probe ⟨𝜎⁢𝑣⟩ values expected from the thermal relic density for TeV DM particles.