Energy-shifted lines in XMM-Newton spectra of Seyfert Galaxies

In the recent literature on AGNs it has been often reported that spectra of Seyfert 1 Galaxies show resonant absorption lines of Fe K which are redshifted from the rest frame position. Such lines are often found with marginal significance but, if real, could potentially open up new avenues to study the circumnuclear gas in the black hole environment. It is also extremely important to take them into account in X-ray spectral analysis because of the influence they have in the correct estimation of spectral parameters, Fe K alpha line in primis. An XMM-Newton observation of Mrk 335 is reported here as a case study: a narrow feature has been detected at 5.9 keV, i.e. with a redshift corresponding to a velocity of v ~ 0.15c. Preliminary results on the statistical significance of narrow absorption and emission lines in a sample of PG QSOs observed by XMM-Newton are also included.