VLBA Observations of Neutrino-Candidate Blazars

• Applicant: Professor Dr. Matthias Kadler
• Subject Area: Astrophysics and Astronomy
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 447572188

In the past four years, observational evidence has started piling up that some high-energy cosmic neutrinos detected by the IceCube observatory may be associated with blazars. Indeed, these powerful jets ejected from the centers of active galactic nuclei and pointed at a small angle to our line of sight have long been predicted to be bright neutrino emitters and to exhibit a neutrino spectrum flat enough to exceed the atmospheric background at sufficiently high energies above about 100 TeV. The most prominent example is the source TXS0506+056 that has been associated at 3-sigma significance with a high-energy IceCube neutrino detected in September 2017. Among all later neutrino-blazar associations, the highest-confidence one is represented by a 'gold-alert' neutrino detected in July 2019 in positional coincidence with the blazar PKS1502+106. We have successfully proposed for Very-Long-Baseline Interferometry (VLBI) observations of TXS 0506+056 and PKS 1502+106 in two separate proposals to the Very Long Baseline Array (VLBA). The observations of the two target sources were successfully performed shortly after the neutrino detections at multiple frequencies between 15 GHz and 86 GHz and in full polarization mode. The goal of this proposal is to obtain funding for a full analysis of the resulting observational data to study the VLBI jet structure of the two candidate neutrino blazars in total intensity and polarisation and to follow up on the evolution of their radio jets on milliarcsecond scales after the neutrino events using our observations and complementary data from the MOJAVE program. The VLBI data and analysis will be used to study blazar neutrino-emission models in which both the gamma radiation and the neutrino production are explained in a two-zone model of a structured jet. These models will be tested and their possible parameter ranges will be constrained by our VLBI data and complementary multi wavelength data.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Eduardo Ros