Excitation of Trapped Waves in Simulations of Tilted Black Hole Accretion Disks with Magnetorotational Turbulence

Abstract

We analyze the time dependence of fluid variables in general relativistic, magnetohydrodynamic simulations of accretion flows onto a black hole with dimensionless spin parameter a/M=0.9. We consider both the case where the angular momentum of the accretion material is aligned with the black hole spin axis (an untilted flow) and where it is misaligned by 15 degrees (a tilted flow). In comparison to the untilted simulation, the tilted simulation exhibits a clear excess of inertial variability, that is, variability at frequencies below the local radial epicyclic frequency. We further study the radial structure of this inertial-like power by focusing on a radially extended band at 118 (M/10Msol)^-1 Hz found in each of the three analyzed fluid variables. The three dimensional density structure at this frequency suggests that the power is a composite oscillation whose dominant components are an over dense clump corotating with the background flow, a low order inertial wave, and a low order inertial-acoustic wave. Our results provide preliminary confirmation of earlier suggestions that disk tilt can be an important excitation mechanism for inertial waves.

8 Pages, 6 Figures, accepted for publication in ApJ

References in corpus (7)

• X-ray Properties of Black-Hole Binaries
• Modelling the behaviour of accretion flows in X-ray binaries
• Global General Relativistic MHD Simulation of a Tilted Black-Hole Accretion Disk
• Light Curves from an MHD Simulation of a Black Hole Accretion Disk
• Epicyclic Motions and Standing Shocks in Numerically Simulated Tilted Black-Hole Accretion Disks
• On an excitation mechanism for trapped inertial waves in discs around black holes
• Quasi-Periodic Oscillations from Magnetorotational Turbulence

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