What is the origin of high-energy neutrinos?

A team of astronomers including Prof Sergei Gulyaev, Tim Natusch, and Stuart Weston of the Institute for Radio Astronomy and Space Research reported the first observations that associate high-energy neutrino emission with a gamma-ray blazar outburst:

Coincidence of a high-fluence blazar outburst with a PeV-energy neutrino event
Nature Physics, 12, 807–814 (2016)
https://www.nature.com/articles/nphys3715

The observations reported in this paper are the first time that a cosmic ray particle (an ultra-high energy neutrino) was identified with an astronomical object (a blazar). It was suspected for long time that they must be quasars/blazars responsible for the most energetic cosmic rays, but never proved observationally. Three astronomical techniques were involved in this discovery: the IceCube Neutrino Telescope in Antarctica, the Fermi Gamma-ray Space Telescope, and the Long Baseline Array of the southern hemisphere radio telescopes, which includes our NZ Warkworth 12-m radio telescope. Participation of our radio telescope in observations allowed to increase spatial resolution of the array, which registered dramatic changes in the structure and brightness of the blazar matching with the neutrino event.