Turbulent Generation of Trapped Oscillations in Black Hole Accretion Disks

We have presented in a previous series of papers a general formalism for calculating the adiabatic oscillations trapped near the inner edge of thin accretion disks that are terminated by a marginally stable orbit. We found that in "diskoseismology" the modes break up into two main classes that are analogous to the p-modes and g-modes of helioseismology. In addition, we considered various growth and damping mechanisms, including parameterized models of viscosity. For strongly anisotropic models the modes were damped.

In this work we consider g-modes in the presence of anisotropic viscosity. These modes, existing near the inner edge of the accretion disk and oscillating predominantly in the vertical direction, have radial extents on the order of 2 GM/c² and frequencies of order 0.03 c³/GM (a period of 10⁶ s for 10⁹ M_sun). We estimate the amplitude of these modes by considering the driving due to an ensemble of incoherent, harmonically oscillating point sources. The strength of these point sources is estimated from turbulence theory. The mode amplitude is then given by a balance between the turbulent emission of energy and the viscous damping of energy.

We then make simple estimates of the modulation of the disk luminosity due to these modes. Since the modes exist in the highly luminous inner region of the disk, modulation of order 0.4% in the R band is possible in some cases. Modulation in the UV bands can be nearly a factor of 10 greater. We consider various observational strategies to maximize the possibility of detection of these modes.