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Indirect Search for WIMP Dark Matter with the MAGIC Telescopes

Camilla Maggio


Albeit there is overwhelming evidence for the paradigm of dark matter (DM) in the Universe, its nature is still an enigma at present day, despite the multiple theories and models proposed, and the various experiments and astrophysical installations searching for its signatures. Among the most promising DM par- ticle candidates beyond the Standard Model of particle physics, the Weakly Interacting Massive Particle (WIMP) is the one that has been investigated most. Predicted to have a mass between few GeV and hundreds of TeV, it fits perfectly in the energy range tested by indirect dark matter searches with Imaging Atmospheric Cherenkov Telescopes. The Florian G ̈obel Major Atmospheric Gamma Imaging Cherenkov (MAGIC) telescopes, located at the Observatorio del Roque de los Muchachos, on the Canary Island of La Palma, perform indirect DM searches for WIMPs since their very beginning. Among the targets observed with the MAGIC telescopes, dwarf spheroidal satellite galaxies (dSphs) and the Galactic Center and halo are the most common, both expected to be embedded in a high DM overden- sity. In this thesis, I present the outcome of indirect WIMP annihilation searches from three different observation targets, and the results obtained by a combi- nation of data from multiple targets. No signal has been observed in any of the four searches. The first object analysed, the globular cluster (GC) M15, is a challenge, given its relatively low DM overdensity predicted and the large systematic uncer- tainties resulting from the current lack of star velocity dispersion profiles at its core. No hint of a signal was found in the analysis of a big MAGIC data set, obtained in the framework of a MAGIC key science program observation campaign. In order to get an estimate of the sensitivities achievable with this type of analyses, four different realizations of the M15 DM density profile were investigated. Statistical upper limits on the velocity-averaged WIMP annihila- tion cross-section have been obtained with the use of the DM profiles provided in publications by the H.E.S.S. and VERITAS experiments (compatible with the upper limits of their respective publications, once re-scaled for the larger MAGIC observation time). Further toy statistical upper limits have been ob- tained taking into account DM density profiles from a convolution of the M15 density profile and its expected non-baryonic matter content. The latter was retrieved from N-body simulations of the M/L ratio in the works of den Brok et al. and Baumgardt et al., and considered DM dominated. The limits retrieved with this method are better than the most promising ones from dSphs, but at the same time systematically unreliable, and provide only a minimum value of the velocity-averaged cross-section attainable in M15, awaiting more precise models on the formation and evolution of GCs, and particularly new kinematic measurements at GCs’ cores. As targets selected for a multi-year observational diversification campaign, car- ried out by the MAGIC collaboration on dSphs, the Draco and Coma Berenices dSphs were observed during the past years and analysed. In this case, reliable 95% CL upper limits on the velocity-averaged WIMP annihilation cross-section have been retrieved, given the absence of a signal, and are presented in this thesis. The data of these two dSphs are also combined with the ones of two other dSphs, previously observed with the MAGIC telescopes, namely Segue 1 and Ursa Major II, in order to achieve the best sensitivity for indirect WIMP DM annihilation searches. The results obtained constitute the MAGIC Collabora- tion legacy in this field, and are the most constraining reached by MAGIC and the most stringent in the ≈ 10-100 TeV WIMP DM mass interval in gamma-ray astrophysics searches so far, reaching upper limits of the order of 10−24 cm3s−1 for the velocity-averaged annihilation cross-section. In the last part of this thesis, the Barcelona Raman LIDAR hardware-related activities, in which I participated, are presented. Considering the necessity of new performing systems to monitor the atmosphere above Imaging Atmo- spheric Cherenkov Telescopes, in the view of a fully operational Cherenkov Telescope Array, a new type of Raman LIDAR has been built. The project is explained and the outcome of a series of tests performed on its components reported.

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