VERITAS observation of a bright very-high-energy gamma-ray flare from 1ES 1959+650
ATel #8148; Reshmi Mukherjee (Barnard College) for the VERITAS Collaboration
on 10 Oct 2015; 01:21 UT
Credential Certification: Reshmi Mukherjee (muk@astro.columbia.edu)
Subjects: Gamma Ray, >GeV, TeV, VHE, AGN, Blazar
The VERITAS Collaboration reports the detection of a bright flare of very-high-energy (VHE; E > 100 GeV) gamma rays from the high-synchrotron-peaked blazar 1ES 1959+650. The activity was first detected on UT date October 8th, 2015 (MJD 57303) and additional observations were performed on October 9th. A preliminary analysis of ~2 hours of data taken during each night revealed a gamma-ray excess at the location of 1ES 1959+650 with a statistical significance of about 30 standard deviations for the first night, and 26 standard deviations for the second night. The average flux of the source above 200 GeV was (1.29 +/- 0.07) x 10^-10 ph cm^-2 s^-1 (equivalent to ~50% of the Crab Nebula flux above the same energy threshold) during the first night, and (1.04 +/- 0.07) x 10^-10 ph cm^-2 s^-1 (~45% Crab Nebula flux) during the second night. A power-law fit to the gamma-ray spectrum of the source between 0.2 and 7 TeV shows a spectral index of approximately 2.5, harder than the archival low state spectral state (e.g. Aliu et al. 2014, ApJ, 797,89). 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 a very-high-energy gamma-ray observatory located at the Fred Lawrence Whipple Observatory in southern Arizona, USA.
