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Temporal studies of X-ray emission from black hole candidates are potentially powerful in discriminating among theoretical models of these systems. High time resolution data provide us with three important diagnostic tools: the power spectral density, the Fourier frequency dependent time lag between energy channels, and the coherence function. Any theoretical model must satisfy at least these three constraints (Vaughan et al. 1994).
In this work we present a simple kinematic model of GX339-4 in its ``Very High State" (Miyamoto et al. 1991). The model, based upon theories of accretion disk instabilities, accurately reproduces the observed power spectral densities and time lags, and makes definite predictions for the coherence function. In addition, the model satisfies the energy constraints governing a possible Compton cloud in the system.
The applicability of this model to other systems and other spectral states will be discussed. Furthermore, the general constraints that the above diagnostic tools provide, especially the coherence function, will be reviewed.
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