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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 anda cold system that partially covers the central source. However, in one of the5 BeppoSAX observations, the spectrum shows two peculiar features. Anabsorption feature is detected around 8.5-9 keV with a statistical significanceof 99.96%. This feature can be fitted either with an absorption edge atE=8.62^{+0.34}_{-0.52} keV with optical depth \tau=0.06\pm0.03 or with anabsorption line with 9.5^{+1.3}_{-0.6} keV, width \sigma=0.95^{+1.2}_{-0.7} keVand EW= 200 eV. In the first case, we associate the feature to highly ionizediron at rest, like FeXXII-FeXXIII (E_{rest}=8.4-8.5 keV). In the second casethe feature could be identified with a blend of FeXXV and FeXXVI lines, with anoutflow velocity v \approx (0.09-0.26)c. This spectrum is also characterized bya substantial reduction of the absorption column density and the coveringfraction of the dual absorber. In particular the column density of the mildlyionized and cold absorbers is \approx 3-5 times lower than observed in theother states, and the covering fraction is reduced by \approx 40 per cent. Wepropose a possible explanation linking the two properties in terms of amulti-phase ionized absorber.Comment: 5 pages, 4 figures. Accepted for publication in Astronomy &  Astrophysics Letter

Clearing up the clouds around NGC 4151: evidence of a highly ionized absorber