SEARCH FOR DARK MATTER ANNIHILATION SIGNALS FROM THE FORNAX GALAXY CLUSTER WITH H.E.S.S

The Fornax galaxy cluster was observed with the Fligh Energy Stereoscopic System for a total live time of 14.5 hr, searching for very high energy (VEIE; E > 100GeV) gamma -rays from dark matter (DM) annihilation. No significant signal was found in searches for point-like and extended emissions. Using several models of the DM density distribution, upper limits on the DM velocity-weighted annihilation cross-section [left angle bracket][sigma][upsilon][right angle bracket] as a function of the DM particle mass are derived. Constraints are derived for different DM particle models, such as those arising from Kaluza-Klein and supersymmetric models. Various annihilation final states are considered. Possible enhancements of the DM annihilation gamma -ray flux, due to DM substructures of the DM host halo, or from the Sommerfeld effect, are studied. Additional gamma -ray contributions from internal bremsstrahlung and inverse Compton radiation are also discussed. For a DM particle mass of 1 TeV, the exclusion limits at 95% of confidence level reach values of [left angle bracket][sigma][upsilon][right angle bracket] super(95%C.L.) ~ 10 super(-23) cm super(3) s super(-1), depending on the DM particle model and halo properties. Additional contribution from DM substructures can improve the upper limits on [left angle bracket][sigma][upsilon][right angle bracket] by more than two orders of magnitude. At masses around 4.5 TeV, the enhancement by substructures and the Sommerfeld resonance effect results in a velocity-weighted annihilation cross-section upper limit at the level of [left angle bracket][sigma][upsilon][right angle bracket] super(95%CL) ~ 10 super(-26) cm super(3) s super(-1).