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X-ray Spectroscopy of Disk Winds in Black Hole X-ray Binaries

Megumi Shidatsu, Maxime Parra

TL;DR

The paper addresses how disk winds are launched in Galactic BHXBs and how their properties evolve with accretion state. It synthesizes pre-XRISM wind observations and presents early XRISM/Resolve results for several BHXBs, leveraging high-resolution Fe K spectroscopy to resolve line profiles and discriminate between launching mechanisms. Key findings include resolved absorption features indicative of bound atmospheres in some high/soft phases, emission-layer phenomena in others, and wind suppression in certain hard states, illustrating the rich phenomenology and state dependence of winds. The work underscores XRISM Resolve's potential to distinguish thermal vs magnetic wind drivers and to illuminate the disk–wind–jet coupling, while emphasizing the need for extensive, multi-epoch, multiwavelength monitoring to achieve a comprehensive understanding.

Abstract

Powerful outflows along the accretion disk, known as disk winds, are sometimes launched in black hole X-ray binaries. These winds often manifest themselves in X-ray spectra as blueshifted, highly ionized absorption lines. Previous observations suggest that the mass loss rate from the disk due to disk winds can be comparable to or even more than the mass accretion rate onto the black hole, indicating that disk winds likely play crucial roles in shaping the accretion disk structure and affecting the surrounding environment. However, the mechanisms driving these winds, as well as how their structure changes in response to variations in the mass accretion rate, remain poorly understood. The X-ray Imaging and Spectroscopy Mission (XRISM), launched in September 2023, is equipped with Resolve, a cutting-edge X-ray micro-calorimeter that delivers unprecedented spectral resolution. Resolve is expected to significantly advance our understanding of wind launching mechanisms and their impact on accretion processes and environments. In this article, we review the progress made in the pre-XRISM era, highlight key results obtained from XRISM observations to date, and outline future prospects.

X-ray Spectroscopy of Disk Winds in Black Hole X-ray Binaries

TL;DR

The paper addresses how disk winds are launched in Galactic BHXBs and how their properties evolve with accretion state. It synthesizes pre-XRISM wind observations and presents early XRISM/Resolve results for several BHXBs, leveraging high-resolution Fe K spectroscopy to resolve line profiles and discriminate between launching mechanisms. Key findings include resolved absorption features indicative of bound atmospheres in some high/soft phases, emission-layer phenomena in others, and wind suppression in certain hard states, illustrating the rich phenomenology and state dependence of winds. The work underscores XRISM Resolve's potential to distinguish thermal vs magnetic wind drivers and to illuminate the disk–wind–jet coupling, while emphasizing the need for extensive, multi-epoch, multiwavelength monitoring to achieve a comprehensive understanding.

Abstract

Powerful outflows along the accretion disk, known as disk winds, are sometimes launched in black hole X-ray binaries. These winds often manifest themselves in X-ray spectra as blueshifted, highly ionized absorption lines. Previous observations suggest that the mass loss rate from the disk due to disk winds can be comparable to or even more than the mass accretion rate onto the black hole, indicating that disk winds likely play crucial roles in shaping the accretion disk structure and affecting the surrounding environment. However, the mechanisms driving these winds, as well as how their structure changes in response to variations in the mass accretion rate, remain poorly understood. The X-ray Imaging and Spectroscopy Mission (XRISM), launched in September 2023, is equipped with Resolve, a cutting-edge X-ray micro-calorimeter that delivers unprecedented spectral resolution. Resolve is expected to significantly advance our understanding of wind launching mechanisms and their impact on accretion processes and environments. In this article, we review the progress made in the pre-XRISM era, highlight key results obtained from XRISM observations to date, and outline future prospects.
Paper Structure (11 sections, 4 equations, 2 figures)

This paper contains 11 sections, 4 equations, 2 figures.

Table of Contents

  1. Introduction
  2. Review of X-ray Observations and Interpretations of Winds in BHXBs: before XRISM Era
  3. X-ray Spectroscopy of Winds
  4. Wind Launching Mechanism
  5. XRISM/Resolve Spectroscopy of BHXBs
  6. 4U 1630$-$472: Resolving Absorption Lines in the High/soft State
  7. MAXI J1744$-$294: a Detailed Look at a Galactic-center Source in the High/soft State
  8. IGR J17091$-$3624: High-resolution Spectroscopy in the Low/hard State
  9. V4641 Sgr: Resolving Emission Lines from the Obscured Source
  10. Summary of the Current Status
  11. Summary and Future Prospects

Figures (2)

  • Figure 1: (a) Resolve time-averaged spectrum of 4U 1630$-$472. (b) Resolve spectra in the persistent phase (black) and the dip phase (red), around the Fe K band.
  • Figure 2: Hardness-luminosity diagram showcasing the position and line detections of all XRISM observations of BHXBs with low-mass companions performed as of fall 2025. Transparent markers show the subsample of BHXBs with wind detections in XMM-Newton and Chandra-HETG, from parra2024. The source list is split between objects in that "identified" absorption line sample and the new XRISM observations. Emission lines markers are not scaled with respect to their equivalent width.