X-ray absorption variability in AGN

X-ray absorption variability is a common feature in Active Galactic Nuclei (AGN). Recent works of our group demonstrated that X-ray eclipses, on time scales of a few hours, occurred during several observations of local bright AGNs, without being spotted with traditional, time-averaged spectral analysis. These eclipses are remarkable events in themselves, but, more importantly, are a powerful way to investigate the inner structure of AGNs: they allow to measure the size of the X-ray source and the size, density and geometrical shape of the obscuring clouds. We show that WFXT would provide a real breakthrough in this field, allowing a systematic study of X-ray eclipses on hundreds of sources.