X-ray Spectroscopy of Ionized Obscuration in GRS1915+105 with Chandra and NuSTAR

After a bright, 26-year-long outburst, the black hole binary GRS1915+105 dimmed considerably in 2018 and dropped sharply in flux in 2019. The system has remained in this new, faint "obscured state" ever since. We utilize observations of GRS1915+105 from Chandra and NuSTAR, all performed in July of 2021, to conduct X-ray spectral analysis and photoionization modeling of the obscuring medium. The smooth continuum is consistent with disk emission and Compton scattering from an optically thick hybrid plasma, along with a smeared absorption edge. We find dozens of absorption lines in our Chandra grating spectra, but our measured Doppler shifts show no evidence for a significant outflow. To study these absorption lines further, we perform photoionization modeling using the XSTAR analytic model warmabs; our best fit model requires two partially-covered warmabs components that differ in column density and ionization parameter. Our photoionization analysis suggests that the absorption regions lie in the outer accretion disk. We discuss the implications of this model for the structure of the obscuring medium.