NuSTAR Observations of 52 Compton-thick Active Galactic Nuclei Selected by the Swift/Burst Alert Telescope All-sky Hard X-Ray Survey

Abstract

Abstract We present systematic broadband X-ray spectral analysis of 52 Compton-thick ( 24 ≤ log N H LOS / cm − 2 ) active galactic nucleus (CTAGN) candidates selected by the Swift/Burst Alert Telescope all-sky hard X-ray survey observed with Chandra, X-ray Multi-Mirror Mission-Newton (XMM-Newton), Swift/X-Ray Telescope, Suzaku, and NuSTAR. The XMM-Newton data of 10 objects and the NuSTAR data of 15 objects are published for the first time. We use an X-ray spectral model from a clumpy torus (XClumpy) to determine the torus properties. As a result, the hydrogen column density along the line of sight N H LOS obtained from the XClumpy model indicates that 24 objects are Compton-thin AGNs and 28 objects are CTAGNs in a 90% confidence interval. The main reason is the difference in the torus model applied. The hydrogen column density along the equatorial direction N H Equ of CTAGNs inferred from the XClumpy model is larger than that of less obscured AGNs. The Compton-thin torus covering factor C 22 obtained from the XClumpy model is consistent with that of Ricci et al. in the low Eddington ratio ( log R Edd ≤ − 1.0 ), whereas C 22 inferred from the XClumpy model is larger than that of Ricci et al. in the high Eddington ratio ( − 1.0 ≤ log R Edd ). The average value of the Compton-thick torus covering factor C 24 obtained from the XClumpy model is 36 − 4 + 4 %. This value is larger than that of Ricci et al. ( C 24 ≃ 27 − 4 + 4 %) based on the assumption that all AGNs have intrinsically the same torus structure. These results suggest that the structure of CTAGNs may be intrinsically different from that of less obscured AGNs.