Global Three‐dimensional Magnetohydrodynamic Simulations of Black Hole Accretion Disks: X‐Ray Flares in the Plunging Region

Abstract

We present the results of three-dimensional global resistive magnetohydrodynamic (MHD) simulations of black hole accretion flows. General relativistic effects are simulated by using the pseudo-Newtonian potential. Initial state is an equilibrium model of a torus threaded by weak toroidal magnetic fields. As the magnetorotational instability (MRI) grows in the torus, mass accretes to the black hole by losing the angular momentum. We found that in the innermost plunging region, non-axisymmetric accretion flow creates bisymmetric spiral magnetic fields and current sheets. Mass accretion along the spiral channel creates one armed spiral density distribution. Since the accreting matter carries in magnetic fields which subsequently are stretched and amplified due to differential rotation, current density increases inside the channel. Magnetic reconnection taking place in the current sheet produces slow mode shock waves which propagate away from the reconnection site. Magnetic energy release in the innermost plunging region can be the origin of X-ray shots observed in black hole candidates. Numerical simulations reproduced soft X-ray excess preceding the peak of the shots, X-ray hardening at the peak of the shot, and hard X-ray time lags.

Rapid optical variations correlated with X-rays in the 2015 second outburst of V404 Cygni (GS 2023+338)

“…In the ADAF, the matter moves to the central object with a speed comparable to the free-fall velocity (v ff ) (v f ∼ αv ff ; Narayan & Yi 1995). If the optical fluctuations, which were triggered at a region close to the truncation radius, propagated to the central black hole via the accretion of mass flow on the free-fall timescale in the ADAF, the transition radius is estimated to be ∼2.5-4.0×10 8 [cm] by using the above approximation for α = 0.01 (Sano et al 1998;Machida & Matsumoto 2003) and our estimates of X-ray delays. The estimated value of R tr corresponds to ∼100-150r s .…”

Papaloizou–Pringle instability suppression by the magnetorotational instability in relativistic accretion discs

“…This choice inevitably leads to an initial transient in the simulation, which could in principle favour one instability over the other, and hence put in serious question the validity of the results on the relative importance of PPI and MRI. Moreover, only a very small fraction of previous works (Hawley 2000;Hawley & Krolik 2001;Machida & Matsumoto 2003;Machida, Nakamura & Matsumoto 2004;McKinney, Tchekhovskoy & Blandford 2012) considered models with purely toroidal magnetic fields and the full azimuthal range, which are necessary conditions to study the interaction between the PPI and the (slow) non-axisymmetric MRI in wide tori. There are only a few recent works that employed analytical equilibrium solutions as initial conditions.…”

Three‐dimensional Magnetohydrodynamic Simulations of Jets from Accretion Disks

“…Only a few three-dimensional MHD simulations of jet formation have been presented that solve the disk accretion selfconsistently (e.g., Matsumoto & Shibata 1997, 1999Matsumoto 1999;Kigure et al 2002) although global three-dimensional MHD simulations (not adopting the shearing box approximation) of the accretion disk around the black hole have been vigorously pursued in recent years (e.g., Hawley 2000; Hawley & Krolik 2001;Machida & Matsumoto 2003). In this paper, we study the stability of a jet launched from the accretion disk using threedimensional MHD simulations.…”