XMM-Newton observations reveal the disappearance of the wind in 4U 1630-47

TL;DR

This study uses XMM-Newton observations to track the disappearance of the disc wind in the black hole binary 4U 1630-47 during its outburst, revealing how increasing luminosity ionizes and ultimately eliminates the wind.

Contribution

It provides the first detailed observational evidence linking the ionization state of the disc wind to the accretion state transition in 4U 1630-47.

Findings

The disc wind becomes fully ionized and undetectable as luminosity increases.

The broad iron emission line correlates with wind absorption features and diminishes in the anomalous state.

Reflection fraction decreases with increasing illumination, indicating changes in disc geometry.

Abstract

We report on XMM-Newton observations of the black hole X-ray binary 4U 1630-47 during its 2012-2013 outburst. The first five observations monitor the source as its luminosity increases across the high-soft state of accretion. In the sixth observation the source has made a transition to an "anomalous" state, characterised by a significant contribution of electron scattering. A thermally/radiatively driven disc wind is present in the first four observations, which becomes more photoionised as the luminosity increases with time. In the fifth observation, the wind is not observed any more as a consequence of strong photoionisation and the low sensitivity of this observation. This overall trend is then consistent with a fully ionised wind causing the electron scattering characteristic of the anomalous state in the sixth observation. A broad iron emission line co-exists with the absorption features from the wind in the first four observations but is not visible in the last two observations. We find that the changes in the state of the wind as measured from modelling the absorption features with a self-consistent warm absorber model are correlated to the changes in the broad iron line. When the latter is modeled with a reflection component we find that the reflection fraction decreases as the illumination increases. We propose that the changes in both the absorption and broad emission lines are caused by the increasing luminosity and temperature of the accretion disc along the soft state. Such changes ultimately enable the transition to a state where the wind is fully ionised and consequently Comptonisation plays a significant role.