2025A&A...698L...2P

The radio quasar NVSS J171822+423948 (J1718+4239) was proposed to be the counterpart of the IceCube neutrino event IC-201221A. To reveal the nature of the source, we conducted new very long baseline interferometry observations of this blazar candidate with the Very Long Baseline Array. The observations were carried out in dual-band mode between 4 and 7 GHz. Archival radio data from the literature were also collected for comparison. Our analysis revealed highly variable Doppler-boosted radio emission of the source, with a compact structure at kiloparsec and parsec scales, a slightly inverted spectrum, and a maximum jet inclination angle of θ ≤ 5°. These results confirm that J1718+4239 is a blazar-type object.