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Search for gamma-ray signals from dark matter annihilation or decay at the Draco dwarf galaxy and the Galactic halo with MAGIC

Daniele Ninci


Departament de Física Universitat Autònoma de Barcelona

External urlhttps://www.tdx.cat/bitstream/handle/10803/671280/dani1de1.pdf?sequence=1&isAllowed=y


Astrophysical and cosmological observations affirm the existence of a non-baryonic and invisible form of matter, called Dark Matter, accounting for the 85% of the matter content in the Universe. Among the numerous models, the Weakly Interacting Massive Particle, a class of non-standard model (SM) particles, represents one of the best candidate as DM, as fit the characteristic request by the current cosmological model for DM: weakly interactive with ordinary matter, non-relativistic (cold DM), and stable at cosmological scale. WIMPs particles are supposed to have a mass between few GeV and hundreds of TeV, and to produce SM particles through annihilation or decay. Indirect search for DM signature in the astrophysical γ rays is very promising, since they point directly to the emitting source and γ-ray spectra from DM contains features that are related with no other astrophysical object except DM. Moreover, DM drove the historical evolution of the Universe, since baryonic matter accumulate in the DM over-densities, creating all the structures we see nowadays. Consequently, galaxies, satellite galaxies, and other structures, formed inside a DM halo, with a density peaked towards the center of the Galaxy and decreasing toward the outer region. Milky Way and its dwarf satellite galaxies represent the closest DM dominated objects. In this thesis I present the results from the observations of the Draco dwarf galaxy and the extended region of the Galactic DM halo. These targets have different characteristic: Draco is a moderate-extended source for MAGIC and can be treated with the standard analysis chain, while the halo region is very extended and the expected signal region goes far beyond the MAGIC field of view. The new approach I considered for observing successfully GH, consists in comparing pairs of observations performed at different angular distances from the Galactic Center, selected in such a way that all the diffuse components cancel out, except for those coming from the DM. In order to keep the systematic uncertainty of this novel background estimation method down to a minimum, the observation pairs have been acquired during the same nights, follow exactly the same azimuth and zenith paths with excellent weather conditions. A 20% of the data was used to determine the systematic level, while the rest is used to constraint the DM thermally averaged cross-section and/or the lifetime. For both searches, a binned maximum-likelihood analysis optimized for exploiting the spectra feature of DM annihilation and decay, is applied on both data sets. No hints of DM have been found in both data sample, constraining the thermally averaged cross-section down to ~10^−23 cm^3/s and the DM lifetime up to ~10^26 s

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