The 67 Hz feature in the black hole candidate GRS 1915+105 as a possible ''diskoseismic'' mode

The Rossi X-Ray Timing Explorer has made feasible for the first time the search for high-frequency (greater than or similar to 100 Hz) periodic features in black hole candidate (BHC) systems. Such a feature, with a 67 Hz frequency, recently has been discovered in the BHC GRS 1915+105 (Morgan, Remillard, & Greiner). This feature is weak (rms variability similar to 0.3%-1.6%), stable in frequency (to within similar to 2 Hz) despite appreciable luminosity fluctuations, and narrow (quality factor Q similar to 20). Several of these properties are what one expects for a ''diskoseismic'' g-mode in an accretion disk about a 10.6 M. (nonrotating) to 36.3 M. (maximally rotating) black hole (if we are observing the fundamental-mode frequency). We explore this possibility by considering the expected luminosity modulation, as well as possible excitation and growth mechanisms-including turbulent excitation, damping, and ''negative'' radiation damping. We conclude that a diskoseismic interpretation of the observations is viable.