Compton-thick AGN in the NuSTAR era III: A systematic study of the torus
  covering factor
  We present the analysis of a sample of 35 candidate Compton thick (CT-)
active galactic nuclei (AGNs) selected in the nearby Universe (average redshift
<z>~0.03) with the Swift-BAT 100-month survey. All sources have available
NuSTAR data, thus allowing us to constrain with unprecedented quality important
spectral parameters such as the obscuring torus line-of-sight column density
(N_{H, z}), the average torus column density (N_{H, tor}) and the torus
covering factor (f_c). We compare the best-fit results obtained with the widely
used MyTorus (Murphy et al. 2009) model with those of the recently published
borus02 model (Balokovic et al. 2018) used in the same geometrical
configuration of MyTorus (i.e., with f_c=0.5). We find a remarkable agreement
between the two, although with increasing dispersion in N_{H, z} moving towards
higher column densities. We then use borus02 to measure f_c. High-f_c sources
have, on average, smaller offset between N_{H, z} and N_{H, tor} than low-f_c
ones. Therefore, low f_c values can be linked to a "patchy torus" scenario,
where the AGN is seen through an over-dense region in the torus, while high-f_c
objects are more likely to be obscured by a more uniform gas distribution.
Finally, we find potential evidence of an inverse trend between f_c and the AGN
2-10 keV luminosity, i.e., sources with higher f_c values have on average lower
luminosities.
