089070

Studies of heavily obscured active galactic nuclei openParAGNclosePar suggest that the torus that causes the obscuration is patchy comma rather than uniform. The line-of-sight column density openParNH_losclosePar of the obscuring material should vary over weeks to months comma but such an evidence has been observed only in a few X-ray detected AGN comma due to lack of large samples of heavily obscured AGN with multi-epoch observations. We propose for a XMM monitoring of NGC 1358 comma a nearby Compton thick openParCT-closePar AGN with small torus covering factor and NH_los significantly larger than the torus average column density. Through this monitoring comma we expect to measure significant variability in NH_los and detect a transition from CT- to Compton thin comma thus improving our knowledge on the properties of the obscuring material surrounding AGN.