ALMA/NICER observations of GRS 1915+105 indicate a return to a hard state

Abstract

GRS 1915+105 is a transient black hole X-ray binary consistently emitting 10-100% of the Eddington luminosity in the X-ray band during the last three decades until mid-2018 when the source luminosity suddenly decreased by an order of magnitude. This phase was followed by a change to a state with even lower average X-ray fluxes never seen before during the outburst but presenting renewed flaring activity at different wavelengths. Nevertheless, the mean fluxes were still in decline. GRS 1915+105 has the longest orbital period known among low-mass X-ray binaries, the largest accretion disk size, and therefore the largest mass supply for accretion. The high inclination of the disk allows the study of geometrical effects of the accretion flow such as changes in the height-to-radius ratio or the effect of accretion disk winds on the intrinsic emission that are expected during the outburst decay. In addition, the transient jet is expected to change to a compact, self-absorbed, steady jet. We conducted two full polarization Atacama Large Millimeter Array observations to study the jet properties during the outburst decay by analyzing the spectral, polarization, and intra-epoch variability for both observation epochs. In addition, we analyzed nearly daily Neutron Star Interior Composition Explorer pointing observations consisting of modeling X-ray power spectral densities, spectral energy distributions, and lightcurves with a physically motivated model to follow the changing accretion disk properties throughout the outburst decay and relating them to the jet emission. We show that the X-ray and mm spectral, timing, and polarization properties are consistent with those of a typical decaying X-ray binary outburst and that GRS 1915+105 has descended into the low-luminosity hard X-ray state.

18 pages, 11 figures, 5 tables. Accepted for publication in A&A. Abstract abridged to meet ArXiv size limit

References in corpus (14)

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• Radio monitoring of the hard state jets in the 2011 outburst of MAXI J1836-194
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• Observations of a radio-bright, X-ray obscured GRS 1915+105
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• A NICER View of a Highly-Absorbed Flare in GRS 1915+105
• Mass transfer during low mass X-ray transient decays
• Evidence for deceleration in the radio jets of GRS1915+105?
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Cited by in corpus (10)

• Observations of a radio-bright, X-ray obscured GRS 1915+105
• The INTEGRAL view on Black Hole X-ray Binaries
• Matter ejections behind the highs and lows of the transitional millisecond pulsar PSR J1023+0038
• Unraveling the foretime of GRS 1915+105 using AstroSat observations: Wide-band spectral and temporal characteristics
• Sub-second periodic radio oscillations in a microquasar
• Discovering the Mass-Scaled Damping Timescale from Microquasars to Blazars
• Microquasar jet-cocoon systems as PeVatrons
• Dimming GRS 1915+105 observed with NICER and Insight--HXMT
• Likely detection of magnetic field related LFQPO in the soft X-ray re-brightening of GRS~1915+105
• QPOML: A Machine Learning Approach to Detect and Characterize Quasi-Periodic Oscillations in X-ray Binaries