Thermally-Driven Disc Winds as a Mechanism for X-ray Irradiation Heating in Black Hole X-ray Binaries: The Case Study of GX339-4
Abstract
Observed signatures for accretion disc winds in black hole X-ray binaries (BHXBs) are broadly consistent with thermal winds, driven by X-ray irradiation of the outer disc. Thermal winds are known to produce mass outflow rates that can exceed the accretion rate in the disc and have long been postulated as an effective medium to scatter X-rays back onto the disc itself. We study the impact a thermal wind, acting as both a mechanism for mass loss and X-ray irradiation heating, has on the outburst cycles in BHXBs. By modifying the standard disc-instability picture to include wind mass loss and a scattering source of irradiation, simulations suggest mass loss via thermal winds is not a major driver for outburst dynamics in BHXBs and that the more important role these winds may play is as a mechanism for irradiation heating. We apply this idea to ~15 yrs of outburst activity in Galactic BHXB GX339-4. Using simultaneous X-ray and optical observations, we derive properties of a thermal wind, and relate changes in wind properties, source spectrum, and luminosity, to changes in the optical emission that traces the irradiated outer disc. While our findings suggest the observations require a scattering source of irradiation (i.e., disc wind) to play a prominent role, they cannot be fully explained via X-rays scattered in a thermal wind and/or direct X-rays from a central source. This suggests an additional wind launching mechanism, such as magnetic-driving, may also be present. While, overall, wind-driven irradiation is likely to be a common feature among long-period BHXBs, the (primary) driving mechanism(s) behind the wind remain unclear and may even be source dependent.
- Publication:
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American Astronomical Society Meeting Abstracts #235
- Pub Date:
- January 2020
- Bibcode:
- 2020AAS...23515906T