Observations of Milky Way dwarf spheroidal galaxies with the Fermi-large area telescope detector and constraints on dark matter models

We report on the observations of 14 dwarf spheroidal galaxieswith the Fermi Gamma-Ray Space Telescopetaken during the first 11 months of survey mode operations. The Fermi telescope provides a new opportunity to test particle dark mattermodels through the expected gamma-rayemission produced by pair annihilationof weakly interacting massive particles( WIMPs). Local Group dwarf spheroidal galaxies, the largest galactic substructures predicted by the cold dark matterscenario, are attractive targets for such indirect searches for dark matterbecause they are nearby and among the most extreme dark matterdominated environments. No significant gamma-rayemission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the gamma-rayflux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10^-9 photons cm^-2 s^-1. Using recent stellar kinematicdata, the gamma-ray flux limitsare combined with improved determinations of the dark matterdensity profile in 8 of the 14 candidate dwarfs to place limits on the pair annihilationcross-section of WIMPsin several widely studied extensions of the standard model. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matterdensity and WIMPs( neutralinoshere) are dominantly produced non-thermally, e.g. in models where supersymmetry breakingoccurs via anomaly mediation. The gamma-raylimits presented here also constrain some WIMPmodels proposed to explain the Fermi and PAMELA e^+e^- data, including low-mass wino-like neutralinosand models with TeV masses pair- annihilatinginto muon-antimuon pairs. ( Abridged)