Transmission- to reflection-dominated transition in Seyfert 2 galaxies:   the XMM-Newton view
  In this paper we present the current status of a XMM-Newton program to observe an optically-defined, complete and unbiased sample of Compton-thick Seyfert 2 galaxies. The main goal of this project is the measurement of the occurrence rate of transition between transmission- (i.e.: Compton-thin), and reflection-dominated spectral states. These transitions potentially provide information on the distribution of the obscuring matter surrounding the nucleus, and on the duty-cycle of the AGN activity. With about 2/3 of the whole sample being observed, we detected 1 further transition out of 8 observed objects, confirming previous suggestions that these transitions occur on time-scales ~50-100 years. 
M.Guainazzi (1), P.Rodriguez-Pascual (1), A.C.Fabian (2), K.Iwasawa   (2), G.Matt (3), F.Fiore (4) ((1) XMM-Newton SOC, VILS...