Letter to the Editor

Zooming into the neutrino-associated blazar candidate J1718+4239

¹ Konkoly Observatory, HUN-REN Research Centre for Astronomy and Earth Sciences, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
² CSFK, MTA Centre of Excellence, Konkoly-Thege Miklós út 15-17, 1121 Budapest, Hungary
³ Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁴ Department of Astronomy, Institute of Physics and Astronomy, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁵ HUN-REN–ELTE Extragalactic Astrophysics Research Group, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁶ Institute of Astronomy, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudzidzka 5, 87-100 Toruń, Poland
⁷ Theoretical Physics IV, Faculty for Physics & Astronomy, Ruhr University Bochum, D-44780 Bochum, Germany
⁸ Faculty for Physics & Astronomy, Astronomical Institute, Ruhr University Bochum, D-44780 Bochum, Germany
⁹ Ruhr Astroparticle and Plasma Physics Center, Ruhr-Universität Bochum, D-44780 Bochum, Germany

^⋆ Corresponding author: perger.krisztina@csfk.org

Received: 16 April 2025
Accepted: 9 May 2025

Abstract

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.