Compton thick AGN in the NuSTAR era

Abstract

We present the 2-100 keV spectral analysis of 30 candidate Compton thick (CT-) active galactic nuclei (AGN) selected in the Swift-BAT 100-month survey. The average redshift of these objects is $\langle z\rangle\sim$0.03 and they all lie within $\sim$500 Mpc. We used the MyTorus (Murphy et al. 2009) model to perform X-ray spectral fitting both without and with the contribution of the NuSTAR data in the 3-50 keV energy range. When the NuSTAR data are added to the fit, 14 out of 30 of these objects (47% of the whole sample) have intrinsic absorption N$_{\rm H}<10^{24}$ cm$^{-2}$ at the $>$3$\sigma$ confidence level, i.e., they are re-classified from Compton thick to Compton thin. Consequently, we infer an overall observed fraction of CT-AGN with respect to the whole AGN population lower than the one reported in previous works, and as low as $\sim$4%. We find evidence that this over-estimation of N$_{\rm H}$ is likely due to the low quality of a subsample of spectra, either in the 2-10 keV band or in the Swift-BAT one.