  The Seyfert 1 galaxy NGC4151 is characterized by complex X-ray absorption,
well described by a dual absorber, composed of a uniform mildly ionized gas and
a cold system that partially covers the central source. However, in one of the
5 BeppoSAX observations, the spectrum shows two peculiar features. An
absorption feature is detected around 8.5-9 keV with a statistical significance
of 99.96%. This feature can be fitted either with an absorption edge at
E=8.62^{+0.34}_{-0.52} keV with optical depth \tau=0.06\pm0.03 or with an
absorption line with 9.5^{+1.3}_{-0.6} keV, width \sigma=0.95^{+1.2}_{-0.7} keV
and EW= 200 eV. In the first case, we associate the feature to highly ionized
iron at rest, like FeXXII-FeXXIII (E_{rest}=8.4-8.5 keV). In the second case
the feature could be identified with a blend of FeXXV and FeXXVI lines, with an
outflow velocity v \approx (0.09-0.26)c. This spectrum is also characterized by
a substantial reduction of the absorption column density and the covering
fraction of the dual absorber. In particular the column density of the mildly
ionized and cold absorbers is \approx 3-5 times lower than observed in the
other states, and the covering fraction is reduced by \approx 40 per cent. We
propose a possible explanation linking the two properties in terms of a
multi-phase ionized absorber.
