Observations of the Blazar 3c 66a with the Magic Telescopes in Stereoscopic Mode

We report new observations of the intermediate-frequency peaked BL Lacertae object 3C 66A with the MAGIC telescopes. The data sample we use were taken in 2009 December and 2010 January, and comprises 2.3 hr of good quality data in stereoscopic mode. In this period, we find a significant signal from the direction of the blazar 3C 66A. The new MAGIC stereoscopic system is shown to play an essential role for the separation between 3C 66A and the nearby radio galaxy 3C 66B, which is at a distance of only 6. The derived integral flux above 100GeV is 8.3% of Crab Nebula flux and the energy spectrum is reproduced by a power law of photon index 3.64± 0.39stat ± 0.25sys. Within errors, this is compatible with the one derived by VERITAS in 2009. From the spectra corrected for absorption by the extragalactic background light, we only find small differences between the four models that we applied, and constrain the redshift of the blazar to z < 0.68. Subject headings: BL Lacertae objects: individual (3C 66A) – galaxies: active – gamma rays: galaxies [email protected], [email protected] a IFAE, Edifici Cn., Campus UAB, E-08193 Bellaterra, Spain b INAF National Institute for Astrophysics, I-00136 Rome, Italy c Università di Siena, and INFN Pisa, I-53100 Siena, Italy d Technische Universität Dortmund, D-44221 Dortmund, Germany e Universidad Complutense, E-28040 Madrid, Spain f Università di Padova and INFN, I-35131 Padova, Italy g Institute de Astrof́ısica de Canarias, E-38200 La Laguna, Tenerife, Spain h Depto. de Astrof́ısica, Universidad de La Laguna, E-38206 La Laguna, Spain i University of Lódź, PL-90236 Lodz, Poland j Tuorla Observatory, University of Turku, FI-21500 Piikkiö, Finland k Deutsches Elektronen-Synchrotron (DESY), D-15738 Zeuthen, Germany l ETH Zurich, CH-8093 Switzerland m Max-Planck-Institut für Physik, D-80805 München, Germany n Universitat de Barcelona (ICC/IEEC), E-08028 Barcelona, Spain o Universität Würzburg, D-97074 Würzburg, Germany p Università di Udine, and INFN Trieste, I-33100 Udine, Italy q Institut de Ciències de l’Espai (IEEC-CSIC), E-08193 Bellaterra, Spain r Institute de Astrof́ısica de Andalućıa (CSIC), E-18080 Granada, Spain s Croatian MAGIC Consortium, Institute R. Boskovic, University of Rijeka and University of Split, HR-10000 Zagreb, Croatia t Universitat Autònoma de Barcelona, E-08193 Bellaterra, Spain u Institute for Nucl. Research and Nucl. Energy, BG-1784 Sofia, Bulgaria v INAF/Osservatorio Astronomico and INFN, I-34143 Trieste, Italy w ICREA, E-08010 Barcelona, Spain x Università di Pisa, and INFN Pisa, I-56126 Pisa, Italy * Supported by INFN Padova, Italy. ** Now at Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas, Madrid, Spain. *** Now at Finnish Centre for Astronomy with ESO (FINCA), Turku, Finland.