A thermal wind model for the X-ray outflow in GRO J1655-40

Recent Chandra observations of an outflowing gas in GRO J1655-40 resulted in a suggestion by Miller et al. that the wind in this system must be powered by a magnetic process that can also drive accretion through the disk around the black hole. The alternative explanations, of radiation pressure or thermally driven flows, were considered unsatisfactory because of the highly ionized level of the gas and because of the derived small distance from the black hole, well inside the minimum distance required for an efficient X-ray-heated wind. The present Letter shows that there is a simple photoionized wind solution for this system where the gas is much farther out than assumed by Miller et al., at r/r(g) = 10(4.7)-10(5.7). The expected wind velocity, as well as the computed equivalent widths of more than 50 absorption lines in this single-component one-dimensional model, are all in good agreement with the Chandra observations.