THE NuSTAR EXTRAGALACTIC SURVEYS: X-RAY SPECTROSCOPIC ANALYSIS OF THE BRIGHT HARD-BAND SELECTED SAMPLE

We discuss the spectral analysis of a sample of 63 Active Galactic Nuclei (AGN) detected above a limiting ux of S(8 􀀀 24keV) = 7 10􀀀14 erg s􀀀1 cm􀀀2 in the multi-tiered NuSTAR Extragalactic Survey program. The sources span a redshift range z = 0􀀀2:1, and have a median redshift ⟨z⟩ = 0:58. The spectral analysis is performed in the broad-band energy range 0.5-24 keV, combining NuSTAR with Chandra and/or XMM-Newton data. As such this constitutes the largest sample of AGN se- lected at > 10 keV to be homogeneously spectrally analyzed at such deep ux levels. Both empirical and physically motivated models are employed to account for the spectral complexity exhibited by the sources. We study the distribution of spectral parameters such as photon index, column density (NH) and re ection parameter, as well as both the unabsorbed and intrinsic coronal 10-40 keV lu- minosities. Heavily obscured (log[NH=cm􀀀2] 23) and Compton Thick (CT; log[NH=cm􀀀2] 24) AGN constitute 30% (19 sources) and 3% (2 sources) of the sample, respectively. The observed NH distribution is in fair agreement with predictions of Cosmic X-ray Background (CXB) popula- tion synthesis models. Properly accounting for the missed fraction of highly obscured AGN in a ux selected sample, we derive the intrinsic NH distribution. The intrinsic CT fraction relative to the total AGN population, is in the range 13-67%. The fraction of obscured and heavily obscured AGN {log(NH=cm􀀀2) 22 and log(NH=cm􀀀2) 23, respectively { show moderate anticorrelations with lu- minosity. These fractions are larger than the fractions of obscured and heavily obscured local (z < 0:1) AGN. Despite the small sample size in relation to the large range in luminosity and redshift probed, this suggests a qualitative agreement with scenarios invoking two different AGN accretion modes.