Disk warping and black hole X-ray binaries I. Tentative unification of low-frequency quasi-periodic oscillations

TL;DR

This paper explores how disk warping caused by frame-dragging effects can explain the variability patterns, including QPOs, observed in black hole X-ray binaries during state transitions.

Contribution

It proposes that disk warping due to Lense-Thirring torques can unify the understanding of different variability components in black hole X-ray binaries.

Findings

Warp presence can explain QPO type transitions during outbursts.

Analytical estimates support the impact of warps on spectral-timing properties.

Warp emergence accounts for evolution of BBN and QPOs during state changes.

Abstract

X-ray binaries exhibit complex variability patterns studied in the power-spectrum. These include the broad-band noise (BBN) components and various types of narrow components called quasi-periodic oscillations (QPOs). There is currently no consensus about either what determines the presence/absence of the BBN or what generates the QPOs. Many believe the latter is due to frame-dragging effects caused by Lense-Thirring torques. We wish to investigate the potential impact of those frame-dragging effects on the accretion disk itself. In particular, we focus on its impact on the observed variability and the presence (and types) of QPOs associated. We make analytical estimates to assess the potential presence of a geometric warp in the inner accretion disk during state transitions. We show that the presence of a warp can modify the spectral-timing properties in a way that matches the observed transition between QPO types during outbursts. We also discuss the peculiar case of Cyg X-1, as well as how the hard-to-soft transition could be driven by the warp itself. The (expected) emergence of a warp provides a consistent explanation for the evolution of both the BBN and the QPO properties during state transitions. This offers a first path toward unifying the variability of black hole X-ray binary.