Three-dimensional magneto-hydrodynamic simulations of the formation of the inner torus in black hole accretion flows

摘要

We present the results of formation of the inner torus in black hole accretion flows obtained from three dimensional magneto-hydrodynamic simulations. We focus on the dependence of numerical results on the gas temperature supplied from the outer region. General relativisitc effects are taken into account using the pseudo-Newtonian potential. We ignore the radiative cooling of the accreting gas. The initial state is a torus threaded by a weak azimuthal magnetic field.rnWe found that mass accretion rate and the mass outflow rate strongly depend on the temperature of the initial torus. In the cool model, a constant angular momentum inner torus is formed around 4—8r_s where r_s is the Schwarzschild radius. This radius is near the maximum radius of the radial epyciclic frequency. This inner torus deforms itself from a circle to a crescent quasi-periodically. During this deformation, the mass accretion torus returns to a circular shape and starts the next cycle. The time interval of this deformation is caused by the magnetic dynamo activitis driven by MRI. When the magnetic energy released, magnetic pressure driven outflows blow from the inner torus.rnPower spectral density (PSD) of the time variation of the mass accretion rate in the coolo model has a low frequency peak around 10Hz when we assumed a 10M_⊙ black hole. The PSD of the hot model is flat in 1 - 30Hz. The slope of the PSD in the cool model is steeper than than in the hot model in 30 — 100Hz.