The Luminous, Hard State Can't Be MAD

TL;DR

This paper argues that the luminous, hard state of black hole X-ray binaries cannot always be associated with magnetically arrested discs because of conflicting observational and simulation-based evidence regarding QPOs and disc precession.

Contribution

The paper presents a novel argument linking QPO origins, jet precession, and magnetic field effects to challenge the association of MADs with certain black hole states.

Findings

Type-C QPOs are best explained by Lense-Thirring precession.

Optical and IR QPOs suggest jet precession occurs.

Simulations show MADs suppress Lense-Thirring precession.

Abstract

We present a straightforward argument for why the luminous, hard state of black hole X-ray binaries (BHXRBs) cannot always be associated with a magnetically arrested accretion disc (MAD). It relies on three core premises: 1) that the type-C quasi-periodic oscillation (QPO) is best explained by Lense-Thirring (LT) precession of a tilted, inner, hot flow; 2) that observed optical and infrared (IR) QPOs with the same or lower frequency as the type-C QPO suggest the jet, too, must precess in these systems; and 3) that numerical simulations of MADs show that their strong magnetic fields promote alignment of the disc with the black hole and, thereby, suppress LT precession. If all three premises hold true, then, at least whenever the optical and IR QPOs are observed alongside the type-C QPO, these systems cannot be in the MAD state. Extending the argument further, if the type-C QPO is always associated with LT precession, then it would rule out MADs anytime this timing feature is seen, which covers nearly all BHXRBs when they are in the luminous, hard and hard-intermediate states.