  We compute Fourier-resolved X-ray spectra of the Seyfert 1 Markarian 766 to
study the shape of the variable components contributing to the 0.3-10 keV
energy spectrum and their time-scale dependence. The fractional variability
spectra peak at 1-3 keV, as in other Seyfert 1 galaxies, consistent with either
a constant contribution from a soft excess component below 1 keV and Compton
reflection component above 2 keV, or variable warm absorption enhancing the
variability in the 1-3 keV range. The rms spectra, which shows the shape of the
variable components only, is well described by a single power law with an
absorption feature around 0.7 keV, which gives it an apparent soft excess. This
spectral shape can be produced by a power law varying in normalisation,
affected by an approximately constant (within each orbit) warm absorber, with
parameters similar to those found by Turner et al. for the warm-absorber layer
covering all spectral components in their scattering scenario. The total soft
excess in the average spectrum can therefore be produced by a combination of
constant warm absorption on the power law plus an additional less variable
component. On shorter time-scales, the rms spectrum hardens and this evolution
is well described by a change in power law slope, while the absorption
parameters remain the same. The frequency dependence of the rms spectra can be
interpreted as variability arising from propagating fluctuations through an
extended emitting region, whose emitted spectrum is a power law that hardens
towards the centre. This scenario reduces the short time-scale variability of
lower energy bands making the variable spectrum harder on shorter time-scales
and at the same time explains the hard lags found in these data by Markowitz et
al.
