A long-lived compact jet in the black hole X-ray binary candidate AT2019wey

¹ School of Electronic and Electrical Engineering, Shangqiu Normal University, 298 Wenhua Road, Shangqiu, Henan 476000, PR China
e-mail: hongmin.cao@foxmail.com
² INAF – Istituto di Radioastronomia, Via Gobetti 101, 40129 Bologna, Italy
³ Konkoly Observatory, ELKH Research Centre for Astronomy and Earth Sciences, Konkoly Thege Miklós út 15-17, 1121 Budapest, Hungary
⁴ Institute of Physics, ELTE Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁵ Department of Space, Earth and Environment, Chalmers University of Technology, Onsala Space Observatory, 43992 Onsala, Sweden
⁶ ELTE Eötvös Loránd University, Institute of Geography and Earth Sciences, Department of Astronomy, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁷ ELKH-ELTE Extragalactic Astrophysics Research Group, Eötvös Loránd University, Pázmány Péter sétány 1/A, 1117 Budapest, Hungary
⁸ Xinjiang Astronomical Observatory, Chinese Academy of Sciences, 150 Science 1-Street, Urumqi, Xinjiang 830011, PR China
⁹ Shanghai Astronomical Observatory, Key Laboratory of Radio Astronomy, Chinese Academy of Sciences, 80 Nandan Road, Shanghai 200030, PR China
¹⁰ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China

Received: 17 September 2021
Accepted: 28 October 2021

Abstract

AT2019wey is a transient discovered by the Asteroid Terrestrial-impact Last Alert System survey in December of 2019. Follow-up optical, radio, and X-ray observations led to classification of this source as a Galactic black hole X-ray binary candidate. We carried out one-epoch 6.7 GHz European Very Long Baseline Interferometry Network and two-epoch multi-frequency (1.6, 4.5, 6.7 GHz) Very Long Baseline Array observations within a year after its discovery. These observations reveal a fading and flat-spectrum radio source with no discernible motion. These features suggest the detection of a compact jet. The source appears resolved at milliarcsecond scales, and the source angular size versus frequency trend is consistent with scatter broadening. This allows us to constrain the lower limit of the source distance to 6 kpc if the scattering medium is in a Galactic spiral arm. For a source location at greater than 3 kpc, the estimated upper limit of the peculiar velocity suggests the asymmetric natal kick may have occurred during the black hole formation stage.