X-ray Spectral Variations in the Black Hole Candidate, AT2019wey, and Implications for the Issue of Inner Disk Truncation in Different X-ray States

The black hole binary (BHB) AT2019wey (SRGA J043520.9+552226) has displayed a dozen significant swings in X-ray intensity and colors since NICER monitoring observations began, soon after the X-ray source brightened in 2020 August. We first show new evidence in support of the BHB classification of this source. We then report X-ray spectral analyses in which the inner radius and temperature of the accretion disk follow a distinct track as the source oscillates through the intermediate state, with brief touchdowns into the soft/thermal state, before transitioning into the hard state. In the hard state, variations persist, but with smaller amplitude. Likewise, the accretion corona evolves along a distinct track, when it is characterized by the photon index and the scattering fraction by which disk photons are Compton scattered to form the corona. On the question of inner disk truncation in different X-ray states, the results imply that truncation is confined to within a factor ~3, with maxima occurring in the intermediate state, not the hard state. We compare this to other BHB transients where the state evolution tends to be simple and progressive, rather than repetitive.