NGC454: unveiling a new "changing look" AGN

Abstract

We present a detailed analysis of the X-ray spectrum of the Seyfert 2 galaxy NGC454E, belonging to the interacting system NGC454. Observations performed with Suzaku, XMM-Newton and Swift allowed us to detect a dramatic change in the curvature of the 2-10 keV spectrum, revealing a significant variation of the absorbing column density along the line of sight (from ~ 1 x10^{24}cm^{-2} to ~ 1x10^{23}cm^{-2}). Consequently, we propose this source as a new member of the class of "changing look" AGN, i.e. AGN that have been observed both in Compton-thin (NH =10^{23 cm^{-2}) and reflection dominated states (Compton-thick, NH >10^{24} cm^{-2}). Due to the quite long time lag (6 months) between the Suzaku and XMM-Newton observations we cannot infer the possible location of the obscuring material causing the observed variability. In the 6-7 keV range the XMM-Newton observation also shows a clear signature of the presence of an ionized absorber. Since this feature is not detected during the Suzaku observation (despite its detectability), the simplest interpretation is that the ionized absorber is also variable; its location is estimated to be within ~10^{-3} pc from the central black hole, probably much closer in than the rather neutral absorber.