Letter to the Editor

New jet feature in the parsec-scale jet of the blazar OJ 287 connected to the 2017 teraelectronvolt flaring activity

¹ Instituto de Astrofísica de Andalucía-CSIC, Glorieta de la Astronomía s/n, 18008 Granada, Spain
e-mail: rlico@iaa.es
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ INAF Istituto di Radioastronomia, via Gobetti 101, 40129 Bologna, Italy
⁴ Foundation for Research and Technology – Hellas, IESL & Institute of Astrophysics, Voutes, 7110 Heraklion, Greece
⁵ Department of Physics, University of Crete, 70013 Heraklion, Greece
⁶ Institute for Astrophysical Research, Boston University, 725 Commonwealth Avenue, Boston, MA 02215, USA
⁷ Astronomical Institute, St. Petersburg State University, Universitetskij Pr. 28, Petrodvorets, St. Petersburg 198504, Russia
⁸ Korea Astronomy and Space Science Institute, Daedeok-daero 776, Yuseong-gu, Daejeon 34055, Republic of Korea
⁹ Santa Cruz Institute for Particle Physics and Department of Physics, University of California, Santa Cruz, CA 95064, USA
¹⁰ Physics Department, McGill University, Montreal, QC H3A 2T8, Canada
¹¹ Institut de Radioastronomie Millimétrique, Avenida Divina Pastora 7, Local 20, 18012 Granada, Spain

Received: 18 December 2021
Accepted: 2 February 2022

Abstract

Context. In February 2017 the blazar OJ 287, one of the best super-massive binary-black-hole-system candidates, was detected for the first time at very high energies (VHEs; E > 100 GeV) with the ground-based γ-ray observatory VERITAS.

Aims. Very high energy γ rays are thought to be produced in the near vicinity of the central engine in active galactic nuclei. For this reason, and with the main goal of providing useful information for the characterization of the physical mechanisms connected with the observed teraelectronvolt flaring event, we investigate the parsec-scale source properties by means of high-resolution very long baseline interferometry observations.

Methods. We use 86 GHz Global Millimeter-VLBI Array (GMVA) observations from 2015 to 2017 and combine them with additional multiwavelength radio observations at different frequencies from other monitoring programs. We investigate the source structure by modeling the brightness distribution with two-dimensional Gaussian components in the visibility plane.

Results. In the GMVA epoch following the source VHE activity, we find a new jet feature (labeled K) at ∼0.2 mas from the core region and located in between two quasi-stationary components (labeled S1 and S2). Multiple periods of enhanced activity are detected at different radio frequencies before and during the VHE flaring state.

Conclusions. Based on the findings of this work, we identify as a possible trigger for the VHE flaring emission during the early months of 2017 the passage of a new jet feature through a recollimation shock (represented by the model-fit component S1) in a region of the jet located at a de-projected distance of ∼10 pc from the radio core.