Thermal Disk Winds in X-Ray Binaries: Realistic Heating and Cooling Rates Give Rise to Slow, but Massive, Outflows

Journal Article · Fri Feb 10 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/836/1/42· OSTI ID:22869419

Higginbottom, N.; Knigge, C. ^[1]; Proga, D. ^[2]; Long, K. S. ^[3]

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1. School of Physics and Astronomy, University of Southampton, Highfield, Southampton SO17 1BJ (United Kingdom)
2. Department of Physics and Astronomy, University of Nevada, Las Vegas, 4505 S. Maryland Pkwy, Las Vegas, NV 89154-4002 (United States)
3. Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD, 21218 (United States)

A number of X-ray binaries exhibit clear evidence for the presence of disk winds in the high/soft state. A promising driving mechanism for these outflows is mass loss driven by the thermal expansion of X-ray heated material in the outer disk atmosphere. Higginbottom and Proga recently demonstrated that the properties of thermally driven winds depend critically on the shape of the thermal equilibrium curve, since this determines the thermal stability of the irradiated material. For a given spectral energy distribution, the thermal equilibrium curve depends on an exact balance between the various heating and cooling mechanisms at work. Most previous work on thermally driven disk winds relied on an analytical approximation to these rates. Here, we use the photoionization code cloudy to generate realistic heating and cooling rates which we then use in a 2.5D hydrodynamic model computed in ZEUS to simulate thermal winds in a typical black hole X-ray binary. We find that these heating and cooling rates produce a significantly more complex thermal equilibrium curve, with dramatically different stability properties. The resulting flow, calculated in the optically thin limit, is qualitatively different from flows calculated using approximate analytical rates. Specifically, our thermal disk wind is much denser and slower, with a mass-loss rate that is a factor of two higher and characteristic velocities that are a factor of three lower. The low velocity of the flow—v{sub max}≃200 km s{sup −1}—may be difficult to reconcile with observations. However, the high mass-loss rate—15 × the accretion rate—is promising, since it has the potential to destabilize the disk. Thermally driven disk winds may therefore provide a mechanism for state changes.

• OSTI ID: 22869419
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 836; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
ATMOSPHERES
BINARY STARS
BLACK HOLES
COSMIC X-RAY SOURCES
HYDRODYNAMIC MODEL
HYDRODYNAMICS
MASS TRANSFER
PHOTOIONIZATION
STELLAR WINDS
THERMAL EQUILIBRIUM
THERMAL EXPANSION