  We present the analysis of X-ray spectral varability made on a sample of 7
Seyfert 1 bright galaxies, using XMM-Newton data. From the "XMM-Newton Science
Archive" we selected those bright Seyfert 1 showing one or more prominent
flares in their 2-10 keV light curves. For each of them we extracted spectra in
3 different time intervals: before, during and after the flare. We fitted them
with a simple power law and then shifted a narrow emission and absorption line
template across the 2.5-10 keV data, in order to investigate the presence of
line-like features with a confidence level greater than 99%. Some highly
significant features were detected in 3 out of 7 sources studied. In
particular, the 3 sources, namely PG 1211+143, NGC 4051 and NGC 3783, showed
the presence of a variable emission feature in the 4.5-5.8 keV band,
characterized by an increase of its intensity after the flare peak. Because of
the observed variability pattern, this feature seems to be ascribable to a
reverbered redshifted relativistic component of the Fe K line.
