The Dynamics of Truncated Black Hole Accretion Disks II: Magnetohydrodynamic Case

Abstract

We study a truncated accretion disk using a well-resolved, semi-global magnetohydrodynamic simulation that is evolved for many dynamical times (6096 inner disk orbits). The spectral properties of hard state black hole binary systems and low-luminosity active galactic nuclei are regularly attributed to truncated accretion disks, but a detailed understanding of the flow dynamics is lacking. In these systems the truncation is expected to arise through thermal instability driven by sharp changes in the radiative efficiency. We emulate this behavior using a simple bistable cooling function with efficient and inefficient branches. The accretion flow takes on an arrangement where a "transition zone" exists in between hot gas in the inner most regions and a cold, Shakura $\&$ Sunyaev thin disk at larger radii. The thin disk is embedded in an atmosphere of hot gas that is fed by a gentle outflow originating from the transition zone. Despite the presence of hot gas in the inner disk, accretion is efficient. Our analysis focuses on the details of the angular momentum transport, energetics, and magnetic field properties. We find that the magnetic dynamo is suppressed in the hot, truncated inner region of the disk which lowers the effective $\alpha$-parameter by $65\%$.

18 pgs, 16 figures, accepted for publication in ApJ

References in corpus (14)

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Cited by in corpus (14)

• Global Radiation Magneto-hydrodynamic Simulations of Sub-Eddington Accretion Disks around Supermassive Black Holes
• Formation of Magnetically Truncated Accretion Disks in 3D Radiation-Transport Two-Temperature GRMHD Simulations
• Variable Nature of Magnetically-Driven Ultra-Fast Outflows
• Measuring dynamical masses from gas kinematics in simulated high-redshift galaxies
• The influence of accretion disk thickness on the large-scale magnetic dynamo
• Embedding planetesimals into white dwarf discs from large distances
• A unified accretion disc model for supermassive black holes in galaxy formation simulations: method and implementation
• Global Three-Dimensional Radiation Magnetohydrodynamic Simulations of Accretion onto a Stellar Mass Black Hole at Sub- and Near-critical Accretion Rates
• Magnetic Flux Transport in Radiatively Inefficient Accretion Flows and the Pathway towards a Magnetically Arrested Disk
• Nonthermal emission from the plunging region: a model for the high-energy tail of black hole X-ray binary soft states
• Comparison of SEDs of very massive radio-loud and radio-quiet AGN
• Breathing Oscillations in a Global Simulation of a Thin Accretion Disk
• Stratified Global MHD Models of Accretion Disks in Semi-Detached Binaries
• Effect of Magnetic Field on the Formation of Radiatively Inefficient Accretion Flow around Black Holes