Wind-Fed Magnetic Flux and the Emergence of X-ray Coronae in Active Galactic Nuclei
Abstract
We propose a scenario for the onset of radiatively efficient Active Galactic Nuclei (AGN) in which circumnuclear stellar and supernova-driven winds supply mass and partially ordered magnetic flux to a compact disk reservoir around a supermassive black hole. A coherent poloidal component surviving advection to small radii strengthens inward, lowering the gas plasma beta until mean Maxwell stresses overtake MRI turbulence, compress the disk vertically, and open a magnetically dominated wedge above it. Within a quasi-force-free description of this wedge, the field self-organizes toward a critical twist at which the net radial transport changes sign, defining a magnetic saturation radius rc∼10 rg. The magnetic squeezing of the disk fixes the pressure balance at the interface between the disk and wedge, confining the accumulated flux at rc: flux advected toward this boundary is preferentially shed, fixing Br∝ r−2 in the interior. From the field topology alone we then derive a normalized saturation flux ϕ∼ 50, consistent with the MAD plateau of GRMHD simulations. The resulting compact, time-dependent saturation region is a natural candidate for the AGN X-ray corona, being collisionless, magnetized, and, at high compactness, plausibly pair-rich, with hadronic pair injection providing a conditional additional channel. Its size, variability, and spectral hardness are controlled by rc, the compactness, and the magnetization. We connect these scalings to observed coronal sizes, variability, and the power partition between the corona and jet. We further propose that Little Red and Blue Dots could represent a disk-reservoir phase preceding luminous AGN activity.
Related
- Observed x-ray spectral indices support magnetic buoyancy sourced coronae in Seyfert active galactic nuclei
- Aligned Hierarchical Black Hole Mergers in Active-Galactic-Nuclei Disks Revealed by GWTC-4
- Active galactic nuclei hosting jets. II. Deriving fundamental information from semi-analytical models and the LoTSS sample
- When the Shadow Meets Its Measure: Assessing the Feasibility of Submillimeter Black Hole Shadow Imaging in Megamaser-disk Active Galactic Nuclei
- Evolutionary Map of the Universe (EMU): Selection of active galactic nuclei and star-formation emission with machine-learning techniques
BibTeX
@misc{mbarek2026windfed,
title = {{Wind-Fed Magnetic Flux and the Emergence of X-ray Coronae in Active Galactic Nuclei}},
author = {Rostom Mbarek},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.10681},
eprint = {2610.10681},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.10681},
}
RIS
TY - UNPB
TI - Wind-Fed Magnetic Flux and the Emergence of X-ray Coronae in Active Galactic Nuclei
AU - Rostom Mbarek
PY - 2026
DA - 2026/10/07
PB - arXiv
DO - 10.48550/arxiv.2610.10681
UR - https://arxiv.org/abs/2610.10681
AB - We propose a scenario for the onset of radiatively efficient Active Galactic Nuclei (AGN) in which circumnuclear stellar and supernova-driven winds supply mass and partially ordered magnetic flux to a compact disk reservoir around a supermassive black hole. A coherent poloidal component surviving advection to small radii strengthens inward, lowering the gas plasma beta until mean Maxwell stresses overtake MRI turbulence, compress the disk vertically, and open a magnetically dominated wedge above it. Within a quasi-force-free description of this wedge, the field self-organizes toward a critical twist at which the net radial transport changes sign, defining a magnetic saturation radius r_c∼10 r_g. The magnetic squeezing of the disk fixes the pressure balance at the interface between the disk and wedge, confining the accumulated flux at r_c: flux advected toward this boundary is preferentially shed, fixing B_r∝ r^−2 in the interior. From the field topology alone we then derive a normalized saturation flux ϕ∼ 50, consistent with the MAD plateau of GRMHD simulations. The resulting compact, time-dependent saturation region is a natural candidate for the AGN X-ray corona, being collisionless, magnetized, and, at high compactness, plausibly pair-rich, with hadronic pair injection providing a conditional additional channel. Its size, variability, and spectral hardness are controlled by r_c, the compactness, and the magnetization. We connect these scalings to observed coronal sizes, variability, and the power partition between the corona and jet. We further propose that Little Red and Blue Dots could represent a disk-reservoir phase preceding luminous AGN activity.
ER -