NUMERICAL SIMULATIONS OF PULSATIONALLY UNSTABLE ACCRETION DISKS AROUND SUPERMASSIVE BLACK-HOLES

The innermost region of slim accretion disks with standard alpha visco sity is unstable against axisymmetric radial inertial acoustic perturb ations under certain conditions. Numerical simulations are performed i n order to demonstrate behaviors of such unstable disks. It is shown t hat oscillations with the period of approximately 10(-3) (M(BH)/M.) s can be excited near the inner edge of the disks, where M(BH) is the ma ss of the central object. This kind of unstable disks is a possible or igin of the periodic X-ray time variabilities with period of approxima tely 10(4)s observed in a Seyfert galaxy NGC 6814.