VERITAS Detection of an Exceptional VHE Gamma-Ray Flare from BL Lacertae
ATel #9599; Reshmi Mukherjee (Barnard College) for the VERITAS Collaboration
on 5 Oct 2016; 23:20 UT
Credential Certification: Reshmi Mukherjee (muk@astro.columbia.edu)
Subjects: Gamma Ray, >GeV, TeV, VHE, AGN, Blazar
Referred to by ATel #: 9600
On October 5, 2016 UTC (MJD 57666), a bright flare from BL Lacertae (z = 0.069) was detected during routine snapshot monitoring with the VERITAS array of atmospheric Cherenkov telescopes. VERITAS immediately initiated further deep observations for a total of ~3 hours (~4:00 UTC to ~7:00 UTC). A preliminary analysis of these data yields a strong detection (~1800 excess gamma ray events; ~65 standard deviations above the background). The average flux above 200 GeV was (2.30 +\- 0.08) 10^-10 cm^-2 s^-1 or ~100% of the Crab Nebula flux, and varies throughout the observation. The flux rises from an initial value of (1.74 +\- 0.16) 10^-10 cm^-2 s^-1 (~75% of the Crab Nebula flux) during the first 30-minute observation (run), to an eventual peak of (3.31 +\- 0.23) 10^-10 cm^-2 s^-1 (~140% of the Crab Nebula flux) in the run beginning 2 hours later, before decaying to (1.39 +\- 0.16) 10-10 cm^-2 s^-1 (~60% of the Crab Nebula flux) in the final 30-minute run. This is the brightest VHE flux level detected from BL Lac since June 2011 (Arlen et al, 2013 ApJ, 762,92), and a preliminary spectrum shows emission extending up to nearly 2 TeV.
VERITAS will continue to observe BL Lacertae and multi-wavelength observations are encouraged. Questions regarding the VERITAS observations should be directed to Reshmi Mukherjee (muk@astro.columbia.edu). 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).
