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

<BR /> Aims We study the non-thermal jet emission of the BL Lac object B3 2247+381 during a high optical state. <BR /> 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) gamma-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 gamma-ray (HE, 0.1-100 GeV) data from the Fermi satellite. <BR /> Results The BL Lac object B3 2247+381 (z = 0.119) was detected, for the first time, at VHE gamma-rays at a statistical significance of 5.6sigma. 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.