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VERITAS Detection of VHE Emission from Ton 599

ATel #11075; Reshmi Mukherjee (Barnard College) for the VERITAS Collaboration
on 18 Dec 2017; 23:16 UT
Credential Certification: Reshmi Mukherjee (muk@astro.columbia.edu)

Subjects: Gamma Ray, TeV, VHE, AGN, Blazar

We report the detection, with VERITAS, of VHE emission (>100 GeV) from the flat-spectrum radio quasar Ton 599, also known as 4C +29.45 and RGB J1156+292. Fermi-LAT has reported on bright gamma-ray flaring activity from Ton 599 between 2017 Oct 28 and Nov 5 (ATel # 10931). An exceptionally large optical-NIR flare was recently observed from Ton 599 (ATel #10949), and the source was detected in VHE (>100 GeV) gamma rays by the MAGIC telescopes on UTC 2017/12/15 (MJD 58102.2) (ATel # 11061).

Ton 599 was observed by VERITAS on 15 and 16 December 2017 (UTC) in response to the Fermi-LAT report, for a total exposure of 150 min. A preliminary analysis of the VERITAS observations yields an excess of about 250 gamma ray events above the background at the position of the blazar, corresponding to a statistical significance of about 10 standard deviations. The corresponding average flux observed on the two nights above 100 GeV is (1.0 ± 0.1) x 10-10 cm-2 s-1, or 16% of the Crab Nebula flux above the same threshold. At a redshift of 0.72, Ton 599 is one of the highest redshift objects detected in the VHE energy range.

VERITAS will continue to observe Ton 599; 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).