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 $1.5\times 10^{-24} cm^3 s^{-1}$ 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.