RELATIVISTIC DISKOSEISMOLOGY: C–MODES AND THE LENSE–THIRRING EFFECT

We will briefly review how we investigate the modes of oscillation trapped within the inner region of accretion disks by the strong-field gravitational properties of a black hole (or a compact, weakly-magnetized neutron star). The focus here will be on the 'corrugation'(c)–modes, nearly incompressible perturbations of the inner disk. The lowest c–mode has an eigenfrequency which corresponds to the Lense–Thirring frequency in the weak-field or slow-rotation limit. Its radial extent is a decreasing function of the angular momentum, so a major part of the disk is excited for slowly rotating black holes. We compare the c and g('gravity ')–mode frequencies with stable frequency features detected in the X-ray power spectra of two galactic 'microquasars'.