A Joint Gamma-ray Search for Dark Matter in Dwarf Spheroidal Galaxies with Fermi-LAT, HAWC, H.E.S.S., MAGIC and VERITAS

Weakly Interacting Massive Particles (WIMPs) in the GeV–TeV mass range could produce gamma rays through self-annihilation or decay, offering potential observational signatures for indirect dark matter (DM) searches. Dwarf spheroidal galaxies (dSphs) of the Milky Way are prime targets for such studies due to their high inferred DM-induced gamma-ray fluxes and minimal astrophysical background. In this contribution, we present the final results of the first constraints on DM annihilation in dSphs obtained by combining data from five leading gamma-ray observatories: the space-based Fermi-LAT (100 MeV–100 GeV), the ground-based H.E.S.S., MAGIC, and VERITAS (100 GeV–10 TeV), and the water Cherenkov detector HAWC (>10 TeV). Each experiment analyzed its respective dataset using a coordinated statistical approach, ensuring a consistent treatment of systematics and background estimation. The individual results were then combined in a joint likelihood analysis, significantly improving sensitivity to potential DM signals. By integrating these independent datasets, we derive stringent upper limits on the velocity-weighted annihilation cross-section $\langle \sigma v \rangle$ over a broad DM mass range of 5 GeV to 100 TeV. The obtained constraints improve with respect to the individual searches by a factor of 2–3, depending on the DM mass and annihilation channel. For instance, the observed 95\% confidence level upper limits for a 2 TeV dark matter particle annihilating into $\tau^+ \tau^-$ pairs range between $1.5\times 10^{-24}$ cm$^3$ s$^{-1}$ and $3.2 \times 10^{-25}$ cm$^3$ s$^{-1}$ depending on the assumed dark matter distributions. These results set some of the most stringent constraints on DM annihilation in dSphs to date, showcasing the power of multi-instrument synergy. Our findings underscore the critical role of cross-collaboration among gamma-ray observatories and establish a methodological framework for future analyses, including those incorporating next-generation gamma-ray and neutrino telescopes.