Two Different Long-Term Behaviors in Black Hole Candidates: Evidence for Two Accretion Flows?

By David M. Smith, W. Heindl, J. Swank. 2001

153 citations recorded by the source corpus.

We discuss the results of long-term hard X-ray monitoring of Galactic black hole candidates 1E 1740.7-2942, GRS 1758-258, Cyg X-1, GX 339-4, and Cyg X-3 with the Rossi X-Ray Timing Explorer. The objects divide into two classes. In the first class, exemplified by Cyg X-1, luminosity and spectral hardness evolve simultaneously. In the second class, the relation is more complicated: the softest spectra occur while the count rate is dropping. Most models of accretion, tailored to Cyg X-1, do not predict the second sort of behavior. One interpretation is a simple model with two simultaneous, independent accretion flows: a thin disk and a hot halo. A drop in the accretion rate affecting both flows would propagate through the halo immediately but might take up to several weeks to propagate through the disk. While the inner halo is thus temporarily depleted compared to the disk, a temporary soft state is expected. This picture is supported by the observation that those sources that show delays (1E 1740.7-2942, GRS 1758-258, and GX 339-4) are expected to have low-mass companions, and those that do not (Cyg X-1, Cyg X-3) are known or thought to have high-mass companions. Low-mass companions imply accretion by Roche lobe overflow, with a high specific angular momentum in the accreting material, and therefore a large disk with a long viscous timescale. Wind accretion from massive companions is expected to result in a much smaller disk and thus little viscous delay.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/d6679d1ebd018c65952e219eec0d96e6c665c66b

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Citations in the corpus

GX 339—4: the distance, state transitions, hysteresis and spectral correlations (2004, background): “The different behaviour of low and high-mass black-hole binaries is likely to be due to different disc sizes (e.g., Smith et al. 2002b).”
Long term variability of Cygnus X-1. I. X-ray spectral-temporal correlations in the hard state (2002, methodology): “…true within the hard state itself – although the Compton corona exists throughout the hard state, phases where a different X-ray spectrum and PSD are observed might well correspond to different coronal geometries (e.g., Nayakshin et al. 2000; Liu et al. 1999; Esin et al. 1997; Smith et al. 2002).”
X-ray Source Populations in Galaxies (2003, background): “The latter type of variability can also be found in a few Galactic XRBs (1E 1740.7–2942, GRS 1758–258, GX 339–4, Smith et al. 2002; see also the XMM-Newton results on GRS 1758-258, Miller et al. 2002).”
Multiwavelength Observations of the 2002 Outburst of GX 339–4: Two Patterns of X-Ray-Optical/Near-Infrared Behavior (2005, background): “The existence of such a second flow has recently been discussed by several authors (van der Klis 2001; Smith et al. 2002a).”
WATCHDOG: A COMPREHENSIVE ALL-SKY DATABASE OF GALACTIC BLACK HOLE X-RAY BINARIES (2015, background): “Periodic modulation has been detected and interpreted as an Porb ∼ 12.7 days, suggesting the object could have a red giant companion (Smith et al. 2002a).”
The Evolution of Black Hole States (2004, background): “A secondary accretion flow (Smith et al., 2002; Yu et al., 2004) or changes in the Compton cooling/heating in the accretion disk corona (MeyerHofmeister et al.”