Landing page for project ES109

The optical transient AT2017bgt is suggested to be a new type of flares from accreting supermassive black holes, characterized by a long-term emission of intensified accretion that remains constant in continuum and emission lines over a period of at least one year. Using the WISE survey data, we have identified the mid-IR outbursts likely associated with UV/optical ones, but found the post-peak mid-IR emission is declined to a quiescent level after a plateau period of about 500 days. By analyzing the VLASS, ASKAP, GMRT and VLBA observations, we find unambiguous evidence of radio brightening and dramatic spectral evolution within ~2 years, possibly due to the evolution of newly-launched synchrotron self-absorbed components. Interestingly, the VLBA observations detect two resolved emission components, which are however evolving rapidly within only half year, the nature of which is unknown. Recent EVN observation at C-band corroborates the resolved structure but reveals significant flux decline. Here we request further EVN observations at the same band, aiming to trace the evolution of resolved structure at mas scales. The data will allow for measuring the proper motion or its upper limit, determining whether it is associated with discrete jet ejections.

This data is part of the archive of VLBI data maintained by JIVE on behalf of the EVN, a network of radio telescopes located primarily in Europe and Asia, with additional antennas in South Africa. The EVN archive itself has the DOI https://doi.org/10.17616/R3Z197