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G. Risaliti, M. Elvis (Harvard-Smithsonian CfA)
We present an analysis of the variation of X-ray absorbing column density in a large sample of Seyfert 2 galaxies. We find that almost all of the sources with multiple X-ray observations show variability in NH on time scales from months to a few years. The lack of correlation between NH and soft X-ray light curves flux suggests that variability of NH is not due to changes in the photoionizing central emission, but most likely is related to variations of the amount of obscuring gas along the line of sight. We discuss the consequences of these results for models of the structure of the circumnuclear regions in AGNs.
The author(s) of this abstract have provided an email address for comments about the abstract: grisaliti@cfa.harvard.edu