VLBA discovery of a resolved source in the candidate black hole X-ray binary AT2019wey

TL;DR

This paper reports VLBA observations of the candidate black hole X-ray binary AT2019wey, revealing a resolved jet consistent with a steady compact jet in the hard X-ray state, with jet power comparable to X-ray luminosity.

Contribution

First VLBA imaging of AT2019wey showing a resolved jet, providing direct evidence of jet formation in this candidate black hole binary.

Findings

Detected a resolved source interpreted as a steady compact jet.

Jet power is comparable to the accretion-disk X-ray luminosity.

Supports the association of the source with a black hole X-ray binary in the hard state.

Abstract

AT2019wey is a Galactic low mass X-ray binary with a candidate black hole accretor first discovered as an optical transient by ATLAS in December 2019. It was then associated with an X-ray source discovered by SRG in March 2020. After observing a brightening in X-rays in August 2020, VLA observations of the source revealed an optically thin spectrum that subsequently shifted to optically thick, as the source continued to brighten in radio. This motivated observations of the source with the VLBA. We found a resolved source that we interpret to be a steady compact jet, a feature associated with black hole X-ray binary systems in the hard X-ray spectral state. The jet power is comparable to the accretion-disk X-ray luminosity. Here, we summarize the results from these observations.