20 years of disk winds in 4U 1630−47

Abstract

Highly ionized X-ray wind signatures have been found in the soft states of high-inclination black hole low mass X-ray binaries (BHLMXBs) for more than two decades. Yet signs of a systematic evolution of the outflow itself along the outburst remain elusive, due to the limited sampling of individual sources and the necessity to consider the broadband evolution of the spectral energy distribution (SED). We performed an holistic analysis of archival X-ray wind signatures in the most observed wind-emitting transient BHLMXB to date, 4U 1630−47. The combination of Chandra, NICER, NuSTAR, Suzaku, and XMM-Newton, complemented in hard X-rays by Swift/BAT and INTEGRAL, spans more than 200 individual days over nine individual outbursts, and provides a near complete broadband coverage of the brighter portion of the outburst. Our results show that the hard X-ray contribution is strongly correlated with the equivalent width (EW) of the lines, and allows one to define “soft” states with ubiquitous wind detections. We then constrained the evolution of the outflow parameters in a set of representative observations, using thermal stability curves and photoionization modeling. The first confirms that the switch to unstable SEDs occurs well after the wind signatures disappear, to the point where the last canonical hard states are thermally stable. The second shows that intrinsic changes in the outflow are required to explain the main correlations of the line EWs, be it with luminosity or the hard X-rays. These behaviors are seen systematically over all outbursts and confirm the longstanding expectation of individual links between the wind properties, the thermal disk, and the corona.