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Discovery of Very High Energy Gamma-Ray Emission from B3 2247+381 by MAGIC

ATEL # 2910; Mose Mariotti (INFN and Univ. of Padova) on behalf of the MAGIC Collaboration
on 7 Oct 2010; 13:02 UT
Password Certification: MosŤ Mariotti (

Subjects: Optical, X-ray, >GeV, AGN
Referred to by ATEL #: 2923

The MAGIC Collaboration reports the discovery of Very High Energy (VHE; >100 GeV) gamma-ray emission from the High Frequency peaking BL Lac object B3 2247+381 with z=0.1187. The source is positionally consistent with the Fermi-LAT gamma-ray source 1FGL J2250.1+3825 (RA 22 50 06.6 dec +38 25 58, J2000), which was flagged as a promising VHE source candidate by the Fermi-LAT collaboration, information which was shared with the MAGIC collaboration (as well as other IACTs) back in October 2009. The MAGIC observations were triggered by an optical high-state of the source, reported by the Tuorla blazar monitoring program ( The VHE detection is based on a 9.3 hour-long observation performed on 2010 September 30th, October 1st, 2nd, 4th, 5th and 6th 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 64 gamma-rays above 150 GeV, corresponding to a pre-trial statistical significance of 5 standard deviations. The observed flux is estimated to be ~2% of the Crab nebula flux above 150 GeV. Target of Opportunity Observations with Swift have also been performed on this source location. A preliminary analysis of the Swift/XRT data shows that the X-ray flux from the source is ~4 times higher than during last observation (spring 2010). Further Swift observations are expected until October 15. We thank the Swift team for accepting and promptly scheduling the X-ray observations. MAGIC will continue observations of B3 2247+381. Observations at other wavelengths are encouraged. Questions regarding the MAGIC observations should be directed to Mose Mariotti (

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