The 67 H[CLC]z[/CLC] Feature in the Black Hole Candidate GRS 1915+105 as a Possible “Diskoseismic” Mode

The Rossi X-ray Timing Explorer (RXTE) has made feasible for the first timethe search for high-frequency (~ 100 Hz) periodic features in black holecandidate (BHC) systems. Such a feature, with a 67 Hz frequency, recently hasbeen discovered in the BHC GRS 1915+105 (Morgan, Remillard, & Greiner). Thisfeature is weak (rms variability ~0.3%-1.6%), stable in frequency (to within ~2Hz) despite appreciable luminosity fluctuations, and narrow (quality factor Q ~20). Several of these properties are what one expects for a ``diskoseismic''g-mode in an accretion disk about a 10.6 M_sun (nonrotating) - 36.3 M_sun(maximally rotating) black hole (if we are observing the fundamental modefrequency). We explore this possibility by considering the expected luminositymodulation, as well as possible excitation and growth mechanisms---includingturbulent excitation, damping, and ``negative'' radiation damping. We concludethat a diskoseismic interpretation of the observations is viable.Comment: 4 Pages, Latex (emulateapj.sty included), to Appear in ApJ Letters, Vol. 477, Final Version with Updated Reference