Accretion disc winds in X-ray binaries

TL;DR

This review summarizes two decades of observational and theoretical research on accretion disc winds in X-ray binaries, highlighting their properties, origins, and significance across multiple wavelengths.

Contribution

It provides a comprehensive synthesis of observational data and theoretical models of accretion disc winds, emphasizing their role in accretion physics and jet interactions.

Findings

Accretion disc winds are common in X-ray binaries across various ionization states.

Winds are closely linked to disc atmospheres and influence accretion processes.

Observations span X-ray, UV, optical, and near-infrared regimes.

Abstract

Despite early theoretical expectations that large-scale, massive outflows would be triggered by accretion onto black holes and neutron stars, their presence was not firmly established until the 2000s. Since then, these accretion disc winds have been recognised as a common, perhaps ubiquitous, feature of accretion discs in X-ray binaries. Over the past two decades, our understanding of these outflows has expanded significantly, with their associated phenomenology now observed across the X-ray, ultraviolet, optical, and near-infrared regimes. In this review, we provide a comprehensive summary of the observational properties of both low- and high-ionisation winds, treating each separately as well as part of a broader phenomenon, and place these findings in the context of current theoretical modelling. We discuss their close connection with disc atmospheres, their impact on the accretion process, and their role within the broader framework that includes the radio jet and the different accretion flow configurations and states. We also address current challenges and outline some of the anticipated developments, particularly those linked to upcoming observational facilities.