Regulation of black-hole accretion by a disk wind during a violent outburst of V404 Cygni

TL;DR

This paper reports the discovery of a unique, large-scale neutral disk wind in the black hole transient V404 Cyg, which significantly influences accretion dynamics and outburst termination.

Contribution

It introduces the first observation of a sustained, neutral outer disk wind in V404 Cyg, revealing its role in regulating black hole accretion during a violent outburst.

Findings

Detected a large, neutral disk wind expanding at 1% of light speed.

Found the wind caused the outburst to end prematurely by depleting the outer disk.

Observed a nebular phase triggered by the wind as accretion sharply drops.

Abstract

Accretion of matter onto black holes is universally associated with strong radiative feedback and powerful outflows. In particular, black hole transients show outflows whose properties are strongly coupled to those of the accretion flow. This includes X-ray winds of ionized material, expelled from the accretion disc encircling the black hole, and collimated radio jets. Very recently, a distinct optical variability pattern has been reported in the transient black hole transient V404 Cyg, and interpreted as disrupted mass flow into the inner regions of its large accretion disc. Here, we report on the discovery of a sustained outer accretion disc wind in V404 Cyg, which is unlike any seen previously. We find that the outflowing wind is neutral, has a large covering factor, expands at 1% of the speed of light and triggers a nebular phase once accretion sharply drops and the ejecta become optically thin. The large expelled mass (> 10^-8 Msun) indicates that the outburst was prematurely ended when a sizeable fraction of the outer disc was depleted by the wind, detaching the inner regions from the rest of the disc. The luminous, but brief, accretion phases shown by transients with large accretion discs imply that this outflow is most likely a new fundamental ingredient regulating mass accretion onto black holes.