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

Abstract

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 $N_H=7\times 10^{23}{\mathrm{cm}}^{-2}$. 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.

28 pages, 12 figures. This paper was accepted to the Astrophysical Journal on December 23rd, 2020

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Cited by in corpus (11)

• The INTEGRAL view on Black Hole X-ray Binaries
• Unraveling the foretime of GRS 1915+105 using AstroSat observations: Wide-band spectral and temporal characteristics
• ALMA/NICER observations of GRS 1915+105 indicate a return to a hard state
• Sub-second periodic radio oscillations in a microquasar
• Mapping the X-ray variability of GRS1915+105 with machine learning
• Time resolved spectroscopy of a GRS 1915+105 flare during its unusual low state using AstroSat
• Likely detection of magnetic field related LFQPO in the soft X-ray re-brightening of GRS~1915+105
• A large misalignment between continuous jet and discrete ejecta in microquasar GRS 1915+105 during its obscured phase
• Dimming GRS 1915+105 observed with NICER and Insight--HXMT
• Optical and X-ray Follow-Up to a Globular Cluster Ultraluminous X-ray Source in NGC 4472
• Exploring the accretion-ejection geometry of GRS 1915+105 in the obscured state with future X-ray spectro-polarimetry