| Blazars are among the most energetic objects in the extragalactic sky. These active galaxies host powerful, relativistic jets that are pointed close to the line of sight of the observer emitting strongly from the radio to the gamma-ray regime. Blazars are also considered to be able to produce neutrinos, fundamental particles that are very difficult to detect. Recently, the IceCube collaboration reported the detection of neutrinos which might have an extraterrestrial origin.
The above images show the blazar PKS B1424-418 in different energy regimes between 2011 and 2013. The gamma-ray images (top panel) were obtained with the Fermi Gamma-ray Space Observatory catching the source (in the center of the images) during a very strong outburst. The radio VLBI images (bottom panel) were taken over the same time frame as part of the multiwavelength programme TANAMI which monitors about a 100 active galaxies in the southern hemisphere. The array used by TANAMI comprises the Australian Long Baseline Array and associated telescopes in Chile, South Africa, New Zealand and Antarctica providing very high angular resolution down to about 1 milliarcsecond which corresponds to about 30 light-years for this source. The outburst exhibited by PKS B1424-418 in the radio is the strongest within the TANAMI sample so far.
Intriguingly, the position and the time of the outburst of PKS B1424-418 coincides with the detection of a 2PeV neutrino by the IceCube collaboration (dashed line in the top panel). The energy emitted by PKS B1424-418 across the electromagnetic spectrum is sufficient to produce such a very high-energy neutrino. The study that is published in Nature Physics ("Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event", Kadler et al. 2016) suggests that these events are linked.
|Credits: NASA/DOE/LAT Collaboration (top panel), TANAMI (bottom panel)