Unifying the X-ray coronae and ultra-fast outflows: a PBI-enhanced outflow-based corona model for the inner accretion disc

TL;DR

This paper introduces a novel outflow-based model enhanced by Photon Bubble Instability to unify the understanding of X-ray coronae and Ultra-Fast Outflows in AGNs, successfully explaining observed phenomena and spectral evolution.

Contribution

It presents a new model coupling PBI-enhanced energy transport with MHD-driven mass loading, unifying the origin of coronae and UFOs in AGN inner discs.

Findings

Model reproduces observed UFO wind speeds with high acceleration efficiency.

Spectral evolution matches increased accretion rate leading to cooler, optically thicker coronae.

Supports a slab-like coronal geometry and a common magnetic origin for UFOs and coronae.

Abstract

The fact that luminous X-ray coronae and Ultra-Fast Outflows (UFOs) are both inferred to originate from the innermost regions of active galactic nuclei (AGNs) suggests a deep physical connection between them. However, standard magnetic buoyancy models struggle to transport sufficient energy through the radiation-pressure-dominated inner disc to sustain both the phenomena, creating a theoretical energy deficit. In this work, we propose an outflow-based model with energy transport enhanced by the Photon Bubble Instability (PBI) in the inner region. By coupling this enhanced energy supply with the MHD turbulence-driven mass-loading mechanism appropriate for weakly magnetized standard discs, we solve the dynamical and thermodynamic structure of the corona. We find that the model can successfully launch high speed winds matching observed UFO kinematics provided the mechanical acceleration efficiency is high ($f_{\rm acc}\gtrsim 0.5$). Furthermore, the model naturally reproduces the observed spectral evolution found in AGN coronae: as the accretion rate increases, the corona becomes optically thicker and cooler and produces a softer spectrum. Our results support an extended slab-like coronal geometry and suggest that UFOs and X-ray coronae in the inner discs are manifestations of the same magnetic activity.