Multiwavelength Analysis of the IceCube Neutrino Source Candidate Blazar PKS 1424+240

The true nature of sources of cosmic neutrinos recorded by the Antarctic IceCube Neutrino Detector is still an enigma of high-energy astrophysics. Time-integrated neutrino source searches with the 10 years of IceCube data unfolded neutrino hot-spots of the sky; among them, one is associated with the blazar PKS 1424+240, which is the third most significant neutrino source candidate in the Northern sky. In this paper, we analyze VLBI radio data of PKS 1424+240 taken with the Very Large Baseline Array at 15 GHz as part of the MOJAVE Survey. We generate the adaptively binned gamma-ray light curve of the source, employing Fermi-LAT data between 100 MeV and 300 GeV. We find that the VLBI jet components maintain quasi-stationary core separations at 15 GHz. We find a quiescence and a perturbed phase of the VLBI core of PKS 1424+240, based on that its Doppler factor increased tenfold after 2016 compared to the quiescence phase. We do not find elevated gamma-ray activity after 2016, while archive Swift-XRT measurements show a highly increased 0.3-10 keV X-ray flux in the beginning of 2017. Substantial increase of the activity of the radio core might help us to identify episodes of particle acceleration in lepto-hadronic blazar jets that eventually lead to the emission of high-energy neutrinos.

Automated summary

The true nature of cosmic neutrinos recorded by the IceCube Neutrino Detector in Antarctica is still unknown in high-energy astrophysics. One neutrino hot-spot discovered by searching the 10 years of IceCube data is associated with the blazar PKS 1424+240, making it the third most significant neutrino source candidate in the Northern sky. In this paper, the VLBI radio data of PKS 1424+240 taken at 15 GHz were analyzed, revealing both quiescent and perturbed phases of the VLBI core, and a significant increase in Doppler factor after 2016. The radio core activity may provide insight into particle acceleration in blazar jets, which can lead to the emission of high-energy neutrinos.