Discovery of VHE γ-ray emission from the BL Lacertae object B3 2247+381 with the MAGIC telescopes

¹ IFAE, Edifici Cn., Campus UAB, 08193 Bellaterra, Spain
e-mail: gtto@ifae.es
² Universidad Complutense, 28040 Madrid, Spain
³ INAF National Institute for Astrophysics, 00136 Rome, Italy
⁴ Università di Siena and INFN Pisa, 53100 Siena, Italy
⁵ Technische Universität Dortmund, 44221 Dortmund, Germany
⁶ Università di Padova and INFN, 35131 Padova, Italy
⁷ Inst. de Astrofísica de Canarias, 38200 La Laguna, Tenerife, Spain
e-mail: berger@astro.uni-wuerzburg.de
⁸ Depto. de Astrofísica, Universidad de La Laguna, 38206 La Laguna, Spain
⁹ University of Łódź, 90236 Lodz, Poland
¹⁰ Tuorla Observatory, University of Turku, 21500 Piikkiö, Finland
e-mail: takalo@utu.fi
¹¹ Deutsches Elektronen-Synchrotron (DESY), 15738 Zeuthen, Germany
¹² ETH Zurich, 8093 Zurich, Switzerland
¹³ Max-Planck-Institut für Physik, 80805 München, Germany
¹⁴ Universität Würzburg, 97074 Würzburg, Germany
¹⁵ Universitat de Barcelona (ICC/IEEC), 08028 Barcelona, Spain
¹⁶ Università di Udine and INFN Trieste, 33100 Udine, Italy
¹⁷ Institut de Ciències de l’Espai (IEEC-CSIC), 08193 Bellaterra, Spain
¹⁸ Inst. de Astrofísica de Andalucía (CSIC), 18080 Granada, Spain
¹⁹ Croatian MAGIC Consortium, Rudjer Boskovic Institute, University of Rijeka and University of Split, 10000 Zagreb, Croatia
²⁰ Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
²¹ Inst. for Nucl. Research and Nucl. Energy, 1784 Sofia, Bulgaria
²² INAF/Osservatorio Astronomico and INFN, 34143 Trieste, Italy
²³ Università dell’Insubria, Como, 22100 Como, Italy
²⁴ Università di Pisa, and INFN Pisa, 56126 Pisa, Italy
²⁵ ICREA, 08010 Barcelona, Spain
²⁶ Now at : École polytechnique fédérale de Lausanne (EPFL), Lausanne, Switzerland
²⁷ supported by INFN Padova  
²⁸ Now at: Centro de Investigaciones Energéticas, Medioambientales y Tecnológicas (CIEMAT), Madrid, Spain
²⁹ Now at: Finnish Centre for Astronomy with ESO (FINCA), University of Turku, Finland
³⁰ Istituto Nazionale di Fisica Nucleare, Sezione di Padova, 35131 Padova, Italy
³¹ Dipartimento di Fisica G. Galilei, Università di Padova, 35131 Padova, Italy

Received: 29 August 2011
Accepted: 25 November 2011

Abstract

Aims. We study the non-thermal jet emission of the BL Lac object B3 2247+381 during a high optical state.

Methods. The MAGIC telescopes observed the source during 13 nights between September 30th and October 30th 2010, collecting a total of 14.2 h of good quality very high energy (VHE) γ-ray data. Simultaneous multiwavelength data was obtained with X-ray observations by the Swift satellite and optical R-band observations at the KVA-telescope. We also use high energy γ-ray (HE, 0.1−100 GeV) data from the Fermi satellite.

Results. The BL Lac object B3 2247+381 (z = 0.119) was detected, for the first time, at VHE γ-rays at a statistical significance of 5.6σ. A soft VHE spectrum with a photon index of −3.2 ± 0.6 was determined. No significant short term flux variations were found. We model the spectral energy distribution using a one-zone SSC-model, which can successfully describe our data.