Spectral Variability in the Obscured State of GRS 1915+105

GRS 1915+105 is an X-ray binary consisting of a stellar mass black hole in a wide 33.5-day orbit around a K giant. After nearly 30 years in a bright outburst, GRS 1915+105 underwent a significant drop in luminosity between 2018 and 2019, down to ~1% of its former peak. Likely caused by Compton-thick obscuration, this new state has been named the “obscured state.” NICER has been monitoring the obscured state on a weekly basis. We report our X-ray spectral analysis of 470 NICER observations from the early obscured state, with a focus on quantifying the obscuration and characterizing emission lines. We find a broad range of partial covering fractions (0.4-1) and obscuring column densities (20-300)x10²² cm^-2, along with a strong correlation between these quantities. In addition, we find that the average strength of the iron emission lines decreases with the obscuring column density. We discuss the implications of these results for the location and geometry of the obscuring medium.