The properties of the AGN torus as revealed from a set of unbiased
  NuSTAR observations
  The obscuration observed in active galactic nuclei (AGN) is mainly caused by
dust and gas distributed in a torus-like structure surrounding the supermassive
black hole (SMBH). However, properties of the obscuring torus of the AGN in
X-ray have not been fully investigated yet due to the lack of high-quality data
and proper models. In this work, we perform a broadband X-ray spectral analysis
of a large, unbiased sample of obscured AGN (with line-of-sight column density
23$\le$log(NH)$\le$24) in the nearby universe which has high-quality archival
NuSTAR data. The source spectra are analyzed using the recently developed
borus02 model, which enables us to accurately characterize the physical and
geometrical properties of AGN obscuring tori. We also compare our results
obtained from the unbiased Compton thin AGN with those of Compton-thick AGN. We
find that Compton thin and Compton-thick AGN may possess similar tori, whose
average column density is Compton thick (N$\rm _{H,tor,ave}$
$\sim$1.4$\times$10$^{24}$ cm$^{-2}$), but they are observed through different
(under-dense or over-dense) regions of the tori. We also find that the
obscuring torus medium is significantly inhomogeneous, with the torus average
column densities significantly different from their line-of-sight column
densities (for most of the sources in the sample). The average torus covering
factor of sources in our unbiased sample is c$_f$=0.67, suggesting that the
fraction of unobscured AGN is $\sim$33%. We develop a new method to measure the
intrinsic line-of-sight column density distribution of AGN in the nearby
universe, which we find the result is in good agreement with the constraints
from recent population synthesis models.
