Upper Limits on the Vhe Gamma-ray Emission from the Willman 1 Satellite Galaxy with the Magic Telescope

We present the result of the observation of the ultrafaint dwarf galaxy Willman 1 performed with the 17 m MAGIC telescope during 15.5 hr between March and May 2008. No significant γ-ray emission was found.We derived upper limits of the order of 10 ph cm s on the integral flux above 100 GeV, which we compare with predictions from several of the established neutralino benchmark models in the mSUGRA parameter space. The neutralino annihilation spectra are defined after including the recently quantified contribution of internal bremsstrahlung from the virtual sparticles that mediate the annihilation. Flux boost factors of three orders of magnitude are required even in the most optimistic scenario to match our upper limits. However, uncertainties in the dark matter intrinsic and extrinsic properties (e.g., presence of substructures, Sommerfeld effect) may significantly reduce this gap. Subject headings: MAGIC – Willman 1 – SDSSJ1049+5103 – Dwarf Spheroidal Galaxies a IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain b ETH Zurich, CH-8093 Switzerland c INAF National Institute for Astrophysics, I-00136 Rome, Italy d Universidad Complutense, E-28040 Madrid, Spain e Technische Universität Dortmund, D-44221 Dortmund, Germany f Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain g Max-Planck-Institut für Physik, D-80805 München, Germany h Università di Padova and INFN, I-35131 Padova, Italy i Inst. de Astrof́ısica de Canarias, E-38200 La Laguna, Tenerife, Spain j University of Lódź, PL-90236 Lodz, Poland k Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, Germany l Università di Siena, and INFN Pisa, I-53100 Siena, Italy m Universitat de Barcelona (ICC/IEEC), E-08028 Barcelona, Spain n Universität Würzburg, D-97074 Würzburg, Germany o Depto. de Astrofisica, Universidad, E-38206 La Laguna, Tenerife, Spain p Università di Udine, and INFN Trieste, I-33100 Udine, Italy q Institut de Cienciès de l’Espai (IEEC-CSIC), E-08193 Bellaterra, Spain r Inst. de Astrof́ısica de Andalucia (CSIC), E-18080 Granada, Spain s University of California, Davis, CA-95616-8677, USA t Tuorla Observatory, Turku University, FI-21500 Piikkiö, Finland u Inst. for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria