EVN 6.7 GHz detection of AT2019wey on milliarcsecond scales
Hongmin Cao (Shangqiu Normal University, Shangqiu, China) Marcello Giroletti, Giulia Migliori (Istituto Nazionale di Astrofisica, Italy) Sandor Frey (Konkoly Observatory, Budapest, Hungary) Krisztina Gabanyi (MTA-ELTE Extragalactic Astrophysics Research Group, Budapest, Hungary) Lang Cui (Xinjiang Astronomical Observatory, CAS, China) Jun Yang (Chalmers University of Technology, Sweden) Tao An, Xiaoyu Hong, Bo Xia (Shanghai Astronomical Observatory, CAS, China) Wenda Zhang (Akademie ved Ceske republiky)
AT2019wey is an optical transient discovered on December 7, 2019 from the ATLAS survey (ATLAS19bcxp, Tonry et al, TNS report 54098). Its radio, optical and X-ray properties (ATel #13571, #13921, #13932, #13984, #14000, #14003, #14100) currently favour the hypothesis of a Galactic accreting X-ray binary origin.

On October 17, 2020 we observed the source at 6.7 GHz for 4 hours with the European VLBI Network (EVN, Project code: RSC07). Compact radio emission is significantly detected at the location of the transient on the angular scale of 2-3 milli-arcsec. The measured flux density of the dominant component is 1.35 +/- 0.22 mJy, which is ~6 times higher than the C-band JVLA flux density (~0.2 mJy) measured on May 27, 2020 (ATel #13984) and also brighter than the 6.7-GHz flux density (~0.12 mJy) interpolated from the JVLA observations between 3 and 10 GHz observed on August 2, 2020 (ATel #13921). The brightening in the radio band could be related to an ongoing jet activity, and a multi-band monitoring of this source is encouraged.

We thank the EVN Program Committee for kindly approving the observation request.
radio,optical,x-ray,binary,black hole,transient