Formation of Magnetically Truncated Accretion Disks in 3D Radiation-Transport Two-Temperature GRMHD Simulations

TL;DR

This paper presents advanced 3D radiation-transport GRMHD simulations showing how magnetic flux influences the formation of truncated accretion disks, revealing a two-phase medium with high efficiency and jet production near black holes.

Contribution

First simulation demonstrating the self-consistent formation of truncated disks with magnetic flux, revealing a two-phase medium and high energy efficiency in GRMHD models.

Findings

Magnetic flux determines the truncation radius of the disk.

Formation of a two-phase medium with cold clumps and hot corona.

Energy efficiency exceeds 90%, with jet and wind production.

Abstract

Multi-wavelength observations suggest that the accretion disk in the hard and intermediate states of X-ray binaries (XRBs) and active galactic nuclei (AGN) transitions from a cold, thin disk at large distances into a hot, thick flow close to the black hole. However, the formation, structure and dynamics of such truncated disks are poorly constrained due to the complexity of the thermodynamic, magnetic, and radiative processes involved. We present the first radiation-transport two-temperature general relativistic magnetohydrodynamic (GRMHD) simulations of truncated disks radiating at ~35% of the Eddington luminosity with and without large-scale poloidal magnetic flux. We demonstrate that when a geometrically-thin accretion disk is threaded by large-scale net poloidal magnetic flux, it self-consistently transitions at small radii into a two-phase medium of cold gas clumps floating through a hot, magnetically dominated corona. This transition occurs at a well-defined truncation radius determined by the distance out to which the disk is saturated with magnetic flux. The average ion and electron temperatures in the semi-opaque corona reach, respectively, T_i ~ 10^10K and T_e ~ 5 10^8K. The system produces radiation, powerful collimated jets and broader winds at the total energy efficiency exceeding ~90%, the highest ever energy extraction efficiency from a spinning black hole by a radiatively efficient flow in a GRMHD simulation. This is consistent with jetted ejections observed during XRB outbursts. The two-phase medium may naturally lead to broadened iron line emission observed in the hard state.