VERITAS Detection of VHE Emission from OJ 287

ATel #10051; Reshmi Mukherjee (Barnard College) for the VERITAS Collaboration
on 5 Feb 2017; 02:02 UT
Credential Certification: Reshmi Mukherjee (muk@astro.columbia.edu)

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We report the detection of VHE emission (>100 GeV) from OJ 287 with VERITAS. The source was observed by VERITAS between 1 February and 4 February 2017 (UTC), for a total exposure of 13.0 hours. OJ 287 is an optically bright quasar, known to display quasi-periodicity with roughly 12-year optical cycles (Shi et al., Ap&SS 310, 59, 2007), and is believed to host a binary supermassive black hole (Valtonen et al., ApJ, 643L, 9, 2006). The VERITAS observations were carried out in response to a rising X-ray flux, noted in the X-ray light curve measured by Swift-XRT; see http://www.swift.psu.edu/monitoring/source.php?source=OJ287 (Stroh & Falcone, ApJS, 207, 28, 2013). A preliminary analysis of the VERITAS observations yields an excess of 141 events above the background at the position of the blazar, corresponding to a statistical significance of 5.7 standard deviations. The corresponding flux observed above 100 GeV is (18 +/- 3) x 10^-12 cm^-2 s^-1, or 3% of the Crab Nebula flux above the same threshold. VERITAS measurements of possible enhanced gamma-ray activity on 2017 Feb 1, led to Swift observations on Feb 2 and 3, which showed the source to be in a remarkably high X-ray state at, or near, the same time (Grupe et al., ATel 10043). VERITAS will continue to observe OJ 287; multi-wavelength observations are encouraged. Questions regarding the VERITAS observations should be directed to Reshmi Mukherjee (muk@astro.columbia.edu). Contemporaneous target-of-opportunity observations with the Swift satellite have also been scheduled. VERITAS (Very Energetic Radiation Imaging Telescope Array System) is located at the Fred Lawrence Whipple Observatory in southern Arizona, USA, and is most sensitive to gamma rays between ~85 GeV and ~30 TeV (http://veritas.sao.arizona.edu).