VERITAS Observations of the BL Lac Object TXS 0506+056

A. U. Abeysekara, A. Archer, W. Benbow, R. Bird, A. Brill, R. Brose, J. H. Buckley, J. L. Christiansen, A. J. Chromey, M. K. Daniel, A. Falcone, Q. Feng, J. P. Finley, L. Fortson, A. Furniss, G. H. Gillanders, O. Gueta, D. Hanna, O. Hervet, J. HolderG. Hughes, T. B. Humensky, C. A. Johnson, P. Kaaret, P. Kar, N. Kelley-Hoskins, M. Kertzman, D. Kieda, M. Krause, F. Krennrich, M. J. Lang, P. Moriarty, R. Mukherjee, S. O'Brien, R. A. Ong, A. N. Otte, N. Park, A. Petrashyk, M. Pohl, E. Pueschel, J. Quinn, K. Ragan, P. T. Reynolds, G. T. Richards, E. Roache, C. Rulten, I. Sadeh, M. Santander, S. S. Scott, G. H. Sembroski, K. Shahinyan, J. Tyler, S. P. Wakely, A. Weinstein, R. M. Wells, P. Wilcox, A. Wilhelm, D. A. Williams, T. J. Williamson, B. Zitzer, A. Kaur

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31 Scopus citations


On 2017 September 22, the IceCube Neutrino Observatory reported the detection of the high-energy neutrino event IC 170922A, of potential astrophysical origin. It was soon determined that the neutrino direction was consistent with the location of the gamma-ray blazar TXS 0506+056 (3FGL J0509.4+0541), which was in an elevated gamma-ray emission state as measured by the Fermi satellite. Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations of the neutrino/blazar region started on 2017 September 23 in response to the neutrino alert and continued through 2018 February 6. While no significant very-high-energy (VHE; E > 100 GeV) emission was observed from the blazar by VERITAS in the two-week period immediately following the IceCube alert, TXS 0506+056 was detected by VERITAS with a significance of 5.8 standard deviations (σ) in the full 35 hr data set. The average photon flux of the source during this period was (8.9 1.6) 10-12 cm-2 s-1, or 1.6% of the Crab Nebula flux, above an energy threshold of 110 GeV, with a soft spectral index of 4.8 1.3.

Original languageEnglish (US)
Article numberL20
JournalAstrophysical Journal Letters
Issue number2
StatePublished - Jul 10 2018

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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