The Accretion Disk Wind in the Black Hole GRO J1655-40

TL;DR

This study analyzes the disk wind in black hole GRO J1655-40 using high-resolution X-ray spectra, revealing a wind likely driven by magnetic forces rather than thermal processes, with implications for black hole accretion models.

Contribution

The paper introduces new photoionization models for the spectrum, indicating the wind originates closer to the black hole and has a higher mass flux than thermal models predict.

Findings

Wind originates more than 10 times closer to the black hole.

Wind mass flux is about 1000 times higher than thermal predictions.

Spectral modeling favors high density, high ionization, small inner radius.

Abstract

We report on simultaneous Chandra/HETGS and RXTE observations of the transient stellar-mass black hole GRO J1655-40, made during its 2005 outburst. Chandra reveals a line-rich X-ray absorption spectrum consistent with a disk wind. Prior modeling of the spectrum suggested that the wind may be magnetically driven, potentially providing insights into the nature of disk accretion onto black holes. In this paper, we present results obtained with new models for this spectrum, generated using three independent photoionization codes: XSTAR, Cloudy, and our own code. Fits to the spectrum in particular narrow wavelength ranges, in evenly spaced wavelength slices, and across a broad wavelength band all strongly prefer a combination of high density, high ionization, and small inner radius. Indeed, the results obtained from all three codes require a wind that originates more than 10 times closer to the black hole and carrying a mass flux that is on the order of 1000 times higher than predicted by thermal driving models. If seminal work on thermally-driven disk winds is robust, magnetic forces may play a role in driving the disk wind in GRO J1655-40. However, even these modeling efforts must be regarded as crude given the complexity of the spectra. We discuss these results in the context of accretion flows in black holes and other compact objects.