VLBI radio structure and radio brightening of the high-energy neutrino emitting blazar TXS 0506+056

TL;DR

This paper links the radio brightening and structural features of blazar TXS 0506+056 to its role as a high-energy neutrino source, revealing a helical jet structure and temporal correlation with neutrino detection.

Contribution

It provides detailed VLBI radio structure analysis and temporal correlation between radio flares and neutrino detection, supporting the blazar's identification as a neutrino source.

Findings

Radio brightness increased since January 2016

Peak of the largest flare coincides with neutrino detection

Jet structure suggests a helical jet at small inclination angle

Abstract

We report on the radio brightening of the blazar TXS 0506+056 (at $z=0.3365$), supporting its identification as source of the high-energy (HE) neutrino IC-170922A by the IceCube Neutrino Observatory. MOJAVE/VLBA data indicate its radio brightness abruptly increasing since January 2016. When decomposing the total radio flux density curve (January 2008 - July 2018) provided by the Owens Valley Radio Observatory into eight Gaussian flares, the peak time of the largest flare overlaps with the HE neutrino detection, while the total flux density exhibits a threefold increase since January 2016. We reveal the radio structure of TXS 0506+056 by analysing VLBI data from the MOJAVE/VLBA Survey. The jet-components maintain quasi-stationary core separations. The structure of the ridge line is indicative of a jet curve at the region $0.5\div2$ mas ($2.5\div9.9$ pc projected) from the VLBI core. The brightness temperature of the core and the pc-scale radio morphology support a helical jet structure at small inclination angle ($<8.2^{\circ}$). The jet pointing towards the Earth is key property facilitating multimessenger observations (HE neutrinos, $\gamma$- and radio flares). The radio brightening preceding the detection of a HE neutrino is similar to the one reported for the blazar PKS 0723--008 and IceCube event ID5.