Artistic impression of a stellar mass black hole accreting from a binary companion and the winds emitted from the accretion disk. Credit: Gabriel Pérez Díaz, SMM (IAC). Download Image
During the past week, NuSTAR performed an observation coordinated with the JAXA/NASA/ESA XRISM observatory of the accreting stellar-mass black hole (BH) AT2019wey. AT2019wey is a low-mass X-ray binary (LMXB) system harboring a rapidly spinning BH seen at a low inclination. AT2019wey was first discovered in 2019 as an optical outburst, followed by an X-ray brightening about six months later. Unlike most BH LMXBs which fade on a timescale of a few months to a year, the outburst of AT2019wey remained bright for several years, decaying around the end of 2025. However, around the beginning of 2026, the system started to rebrighten, approaching the similar flux levels as during the original outburst. Despite being observed numerous times by NuSTAR since its first discovery, this joint XRISM-NuSTAR campaign offers a unique probe of this unusual system. In particular the observing program aims to probe tentative claims of X-ray absorption in the Fe band (around 7 keV). Such features are believed to be caused by equatorial ionized outflows (winds) originating from the accretion disk in the system. The novelty of the program comes from the fact that such features are not expected to be observed in low-inclination systems, such as AT2019wey. This study will expand the understanding of the geometry of ionized outflows in X-ray binaries, and of their impact on accretion. Furthermore, by simultaneously leveraging the high-resolution capabilities of XRISM with the broad pass band and sensitivity of NuSTAR, this study will test the impact of the variability of coronal activity on disk winds, and it will enhance the ability to measure properties of the system such as the BH spin, the inclination of the system, elemental abundances, and the ionization and density of the atmosphere of the accretion disk.
During the past week, NuSTAR performed an observation coordinated with the JAXA/NASA/ESA XRISM observatory of the accreting stellar-mass black hole (BH) AT2019wey. AT2019wey is a low-mass X-ray binary (LMXB) system harboring a rapidly spinning BH seen at a low inclination. AT2019wey was first discovered in 2019 as an optical outburst, followed by an X-ray brightening about six months later. Unlike most BH LMXBs which fade on a timescale of a few months to a year, the outburst of AT2019wey remained bright for several years, decaying around the end of 2025. However, around the beginning of 2026, the system started to rebrighten, approaching the similar flux levels as during the original outburst. Despite being observed numerous times by NuSTAR since its first discovery, this joint XRISM-NuSTAR campaign offers a unique probe of this unusual system. In particular the observing program aims to probe tentative claims of X-ray absorption in the Fe band (around 7 keV). Such features are believed to be caused by equatorial ionized outflows (winds) originating from the accretion disk in the system. The novelty of the program comes from the fact that such features are not expected to be observed in low-inclination systems, such as AT2019wey. This study will expand the understanding of the geometry of ionized outflows in X-ray binaries, and of their impact on accretion. Furthermore, by simultaneously leveraging the high-resolution capabilities of XRISM with the broad pass band and sensitivity of NuSTAR, this study will test the impact of the variability of coronal activity on disk winds, and it will enhance the ability to measure properties of the system such as the BH spin, the inclination of the system, elemental abundances, and the ionization and density of the atmosphere of the accretion disk.
Author: Dr. Paul Draghis, Kavli Postdoctoral Fellow at the MIT Kavli Institute for Astrophysics and Space Research.
