Relativistic diskoseismology. II. Analytical results for c-modes

We first briefly review how we investigate the modes of oscillation trapped within the inner region of accretion disks by the strong-field gravitation al properties of a black hole (or a compact, weakly magnetized neutron star ). Then we focus on the "corrugation" (c-) modes, nearly incompressible per turbations of the inner disk. The fundamental c-modes have eigenfrequencies (ordered by radial mode number) which correspond to the Lense-Thirring fre quency, evaluated at the outer trapping radius of the mode, in the slow rot ation limit. This trapping radius is a decreasing function of the black hol e angular momentum, so a significant portion of the disk is modulated only for slowly rotating black holes. The eigenfrequencies are thus strongly inc reasing functions of black hole angular momentum. The dependence of the eig enfrequencies on the speed of sound (or the luminosity) within the disk is very weak, except for slowly rotating black holes.