  The power spectrum of the X-ray fluctuations of accreting black holes often
consists of two broad humps. We quantitatively investigate the hypothesis that
the lower frequency hump orig- inates from variability in a truncated thin
accretion disc, propagating into a large scale-height inner hot flow which, in
turn, itself is the origin of the higher frequency hump. We extend the
propagating mass accretion rate fluctuations model PROPFLUC to accommodate
double hump power spectra in this way. Furthermore, we extend the model to
predict the cross-spectrum between two energy bands in addition to their power
spectra, allowing us to constrain the model using the observed time lags, which
in the model result from both propagation of fluc- tuations from the disc to
the hot flow, and inside the hot flow. We jointly fit soft and hard power
spectrum, and the cross-spectrum between the two bands using this model for 5
Swift X-ray Telescope observations of MAXI J1659-152. The new double hump model
provides a better fit to the data than the old single hump model for most of
our observations. The data show only a small phase lag associated with the low
frequency hump. We demonstrate quan- titatively that this is consistent with
the model. We compare the truncation radius measured from our fits with that
measured purely by spectral fitting and find agreement within a factor of two.
This analysis encompasses the first joint fits of stellar-mass black hole
cross-spectra and power spectra with a single self-consistent physical model.
