The Characterization of the Obscuring Material in the Nearby Changing-look Compton Thick AGN NGC 1358: Results of a Multi-year NuSTAR-XMM-Newton Monitoring

In this talk, I present the results of a multi-epoch monitoring with NuSTAR and XMM-Newton of NGC 1358, a heavily obscured AGN whose properties made it an ideal changing look candidate. The source was indeed found to be highly variable in line-of-sight column density over time-scales from weeks to years, a result that allowed us to confirm its changing-look nature. We also found a tentative anti-correlation between column density and luminosity, which can be understood in the framework of Chaotic Cold Accretion clouds driving recursive AGN feedback. Besides this important result, I will also show how a multi epoch X-ray monitoring is highly effective in simultaneously constraining three otherwise highly degenerate parameters: the torus average column density and covering factor, and the inclination angle between the torus axis and the observer. In summary, he monitoring campaign of NGC 1358 has proven the efficiency of our newly developed method to select candidate NH-variable, heavily obscured AGN, which we plan to soon extend to a larger sample to better characterize the properties of the obscuring material surrounding accreting supermassive black holes, as well as constrain AGN feeding models.