  We present analysis of the long-term X-ray spectral variability of Seyfert
galaxies as observed by Swift, which provides well-sampled observations over a
much larger flux range and a much longer timescale than any other X-ray
observatory. We examine long-term variability of three AGN: NGC 1365 (see
Connolly et al. 2014), Mkn 335 and NGC 5548. At high fluxes, the 0.5-10 keV
spectra soften with increasing flux, as seen previously within the 2-10 keV
band. However, at very low fluxes the sources also become very soft. We have
fitted a number of models to the data and find that both intrinsic luminosity
variability and variable absorption are required to explain the observations.
In some systems, e.g. NGC 1365, the best explanation is a two-component wind
model in which one component represents direct emission absorbed by a disc wind
wind, with the absorbing column inversely proportional to the intrinsic
luminosity, and the second component represents unabsorbed emission reflected
from the wind. In other AGN the situation is more complex.
