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26th of April 2016
Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event
by Phil Edwards (CASS)
The discovery of extraterrestrial very-high-energy neutrinos by the IceCube collaboration in 2013 has launched a quest for the identification of their astrophysical sources. Gamma-ray blazars have been predicted to yield a cumulative neutrino signal exceeding the atmospheric background above energies of 100 TeV, assuming that both the neutrinos and the gamma-ray photons are produced by accelerated protons in relativistic jets. Since the background spectrum falls steeply with increasing energy, the individual events with the clearest signature of being of an extraterrestrial origin are those at PeV energies. Kadler et al. report in Nature Physics that a major outburst of the blazar PKS B1424-418 occurred in temporal and positional coincidence with a PeV-energy neutrino event detected by IceCube. The outburst of PKS B1424-418 provides an energy output high enough to explain the observed PeV event, indicative of a direct physical association.

The images above are VLBI images of PKS B1424-418 made with the Long Baseline Array, comprising telescopes in Australia, New Zealand, South Africa, Chile and Antarctica as part of the TANAMI project. The images show the core region at 8.4 GHz from 2011 Nov, 2012 Sep and 2013 Mar in a uniform color scale. The angular scale of 1 milliarcsecond (mas) corresponds to about 8.3 pc (27 light-years). All contours start at 3.3 mJy/beam and increase logarithmically by factors of 2. The images were convolved with the enclosing beam from all three observations of 2.26 mas x 0.79 mas at a position angle of 9.5 degrees, which is shown in the bottom left. The peak flux density increases from 1.95 Jy/beam (2011 Apr) to 5.62 Jy/beam (2013 Mar).

Reference: Kadler et al. 2016 (incl. P. Edwards, C. Phillips, J. Stevens, and A. Tzioumis from CASS), Nature, in press

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