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We report on the observations of 14 dwarf spheroidal galaxies with the FermiGamma-Ray Space Telescope taken during the first 11 months of survey modeoperations. The Fermi telescope provides a new opportunity to test particledark matter models through the expected gamma-ray emission produced by pairannihilation of weakly interacting massive particles (WIMPs). Local Group dwarfspheroidal galaxies, the largest galactic substructures predicted by the colddark matter scenario, are attractive targets for such indirect searches fordark matter because they are nearby and among the most extreme dark matterdominated environments. No significant gamma-ray emission was detected above100 MeV from the candidate dwarf galaxies. We determine upper limits to thegamma-ray flux assuming both power-law spectra and representative spectra fromWIMP annihilation. The resulting integral flux above 100 MeV is constrained tobe at a level below around 10^-9 photons cm^-2 s^-1. Using recent stellarkinematic data, the gamma-ray flux limits are combined with improveddeterminations of the dark matter density profile in 8 of the 14 candidatedwarfs to place limits on the pair annihilation cross-section of WIMPs inseveral 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 thermalrelic density is below the observed cosmological dark matter density and WIMPs(neutralinos here) are dominantly produced non-thermally, e.g. in models wheresupersymmetry breaking occurs via anomaly mediation. The gamma-ray limitspresented here also constrain some WIMP models proposed to explain the Fermiand PAMELA e^+e^- data, including low-mass wino-like neutralinos and modelswith TeV masses pair-annihilating into muon-antimuon pairs. (Abridged)

Observations of Milky Way Dwarf Spheroidal galaxies with the Fermi-LAT detector and constraints on Dark Matter models