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Heavily Obscured Active Galactic Nuclei in the NuSTAR Era

Presentation #106.04 in the session “AGN (Poster)”.

Published onApr 01, 2022
Heavily Obscured Active Galactic Nuclei in the NuSTAR Era

The obscuration observed in active galactic nuclei (AGNs) is mainly caused by dust and gas distributed in a torus-like structure surrounding the supermassive black hole (SMBH). However, the properties of the obscuring torus of an AGN in X-ray have not yet been fully investigated because of a lack of high-quality data and proper models. We performed a broadband X-ray spectral analysis of a large, unbiased sample of obscured AGNs (with line-of-sight column density 23 < log(NH) < 24) in the nearby Universe for which high-quality archival NuSTAR data are available. The analysis enables us to accurately characterize the physical and geometrical properties of the obscuring tori in those AGNs. We found that Compton-thin and Compton-thick (log(NH) > 24) AGNs may possess similar tori, whose average column density is Compton thick (log(NH,Tor) ~ 24.15), but they are observed through different (under-dense or over-dense) regions in the obscuring tori. We also found that the dusty gas in the obscuring torus is significantly inhomogeneous, with their torus average column densities being significantly different from their line-of-sight column densities (for >80% of the sources in the sample). The average torus covering factor of the sources in our unbiased sample is cf = 0.67, suggesting a fraction of unobscured AGNs in the nearby Universe being ~33%. We developed a new method to measure the intrinsic line-of-sight column density distribution of AGNs in the local Universe, which can contribute to better constrain the population synthesis models.

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