Accretion disc turbulence and the X-ray power spectra of black hole high states

The high state of black hole candidates is characterized by a quasi- thermalemission component at $kT \sim 1$ keV. In addition, this state tends to havevery low variability which indicates that it is relatively stable, at least on{\it short} time scales. Most models of the high state imply that the bulk ofthe emission comes from an optically thick accretion disc; therefore, thisstate may be an excellent laboratory for testing our ideas about the physics ofaccretion discs. In this work we consider the implications of assuming thataccretion disc viscosity arises from some form of turbulence. Specifically, weconsider the simple case of three dimensional hydrodynamic turbulence. It isfound that the coupling of such turbulence to acoustic modes in the disc canalter the disc emission. We calculate the amplitude and frequencies of thismodulation, and we express our results in terms of the X-ray power spectraldensity. We compare our calculations with observations of the black holecandidate GS 1124-683, and show that for certain parameters we can reproducesome of the high frequency power. We then briefly explore mechanisms forproducing the low frequency power, and note the difficulty that a singlevariability mechanism has in reproducing the full range of observedvariability. In addition, we outline ways in which future spacecraft missions-- such as USA and XTE -- can further constrain our model, especially atfrequencies above $\sim 10^2$ Hz.Comment: 19 pages, uuencoded postscript, CITA Preprint 94-