QPEs as Lense-Thirring precession of super-Eddington flows

TL;DR

This paper proposes a model where Lense-Thirring precession of super-Eddington accretion flows around spinning, misaligned black holes explains the periodic X-ray eruptions observed as QPEs, linking black hole spin, accretion rate, and disk precession.

Contribution

It introduces a simple precession-based model for QPEs that incorporates black hole spin, misalignment, and super-Eddington accretion, offering a new explanation for observed X-ray variability.

Findings

Model explains QPE period and brightness within certain parameters.

Qualitative agreement with GR-RMHD simulation spectra and lightcurves.

Identifies challenges in current simulation details.

Abstract

Quasi-periodic eruptions (QPEs) are a recently identified class of X-ray transient associated with tidal disruption events by supermassive black holes, and for which there are multiple possible explanations. In this paper we present a simple model which requires the black hole be spinning, be misaligned with the accretion flow (both conditions of which are almost certainly met) and that the accretion rate is a few times the Eddington limit. We speculate that the resulting Lense-Thirring torques force the disc and entrained outflows to precess, leading to increased X-ray flux when the wind-cone is oriented at lower inclinations to the observer. We test the range of parameters for which this model could explain the period and brightness of the QPE events discovered thus far, and make qualitative comparisons between the observed X-ray spectra and lightcurves to those extracted from GR-RMHD simulations. Overall, we find some areas of promising concordance, and identify challenges related to the details of current simulations.