  We present the variability analysis of a 100 ks XMM-Newton observation of the
Seyfert 1.5 active galaxy NGC 3227. The observation found NGC 3227 in a period
where its hard power-law component displayed remarkably little long-term
variability. This lucky event allows us to observe clearly a soft spectral
component undergoing a large-amplitude but slow flux variation. Using combined
spectral and timing analysis we isolate two independent variable continuum
components and characterize their behavior as a function of timescale. Rapid
and coherent variations throughout the 0.2-10 keV band reveal a spectrally hard
(photon index ~ 1.7-1.8) power law, dominating the observed variability on
timescales of 30 ks and shorter. Another component produces coherent
fluctuations in 0.2-2 keV range and is much softer (photon index ~ 3); it
dominates the observed variability on timescales greater than 30 ks. Both
components are viewed through the same absorbers identified in the
time-averaged spectrum. The combined spectral and timing analysis breaks the
degeneracy between models for the soft excess: it is consistent with a
power-law or thermal Comptonized component, but not with a blackbody or an
ionized reflection component. We demonstrate that the rapid variability in NGC
3227 is intrinsic to continuum-emitting components and is not an effect of
variable absorption.
