Discovery of Very High Energy Gamma-Ray Emission from 1ES 1215+303 by MAGIC

The MAGIC Collaboration reports the discovery of Very High Energy (VHE ; >100 GeV) gamma-ray emission from the BL Lac object 1ES 1215+303 (also known as ON325) with z=0.130 (White et al. 2000 give z=0.237) based on a 5.6 hour-long observation performed from 2011 January 2nd to 5th in stereoscopic mode with the two 17m diameter imaging Cherenkov telescopes on La Palma, Canary Islands, Spain. The preliminary analysis of the MAGIC data using standard cuts yields a detection of 25 gamma-rays above 250 GeV, corresponding to a statistical significance of 5 standard deviations. The observed flux is estimated to be (2.0+/-1.0)% of the Crab nebula flux above 250 GeV. The source has been flagged as a promising VHE source candidate by the Fermi-LAT collaboration in October 2010. The MAGIC observations were triggered by an optical high-state of the source, reported by the Tuorla blazar monitoring program (http://users.utu.fi/kani/1m/ON_325.html). Target of Opportunity Observations with Swift have also been performed. Fast analysis of the data show that in X-rays the flux is almost doubled respect to previous observation (December 2009) but the spectral shape is almost unchanged. We thank the Swift team for accepting and promptly scheduling the X-ray observations. MAGIC observations suggest also a higher state of a known VHE gamma-ray emitter 1ES 1218+304 in the same field of view, from which an excess of above 5 standard deviation was observed. MAGIC will continue observations of both sources. Observations at other wavelengths are encouraged. Questions regarding the MAGIC observations should be directed to Mose Mariotti (mose.mariotti@pd.infn.it).