The Novel Obscured State of the Stellar-mass Black Hole GRS 1915+105

GRS 1915+105 is a stellar-mass black hole that is well known for exhibiting at least 12 distinct classes of X-ray variability and correlated multi-wavelength behavior. Despite such extraordinary variability, GRS 1915+105 remained one of the brightest sources in the X-ray sky. However, in early 2019, the source became much fainter, apparently entering a new accretion state. Here, we report the results of an extensive, year-long monitoring campaign of GRS 1915+105 with the Neil Gehrels Swift Observatory. During this interval, the flux of GRS 1915+105 gradually diminished; the observed count rate eventually dropped by two orders of magnitude. Simple but robust spectral fits to these monitoring observations show that this new state results from the combination of a dramatic and persistent increase in internal obscuration, and a reduced mass accretion rate. The internal obscuration is the dominant effect, with a median value of N-H = 7 x 10(23) cm(-2). In a number of observations, the source appears to be Compton-thick. We suggest that this state should be identified as the obscured state, and discuss the implications of this new (or rarely observed) accretion mode for black holes across the mass scale.

Automated summary

GRS 1915+105 is a stellar-mass black hole known for its diverse X-ray variability, which entered a new accretion state in early 2019, resulting in a significant decrease in flux. The new state is characterized by internal obscuration and reduced mass accretion rate, with implications for black holes across different mass scales.