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The NuSTAR extragalactic survey : average broadband X-ray spectral properties of the NuSTAR-detected AGNs.

Del Moro, A. and Alexander, D. M. and Aird, J. A. and Bauer, F. E. and Civano, F. and Mullaney, J. R. and Ballantyne, D. R. and Brandt, W. N. and Comastri, A. and Gandhi, P. and Harrison, F. A. and Lansbury, G. B. and Lanz, L. and Luo, B. and Marchesi, S. and Puccetti, S. and Ricci, C. and Saez, C. and Stern, D. and Treister, E. and Zappacosta, L. (2017) 'The NuSTAR extragalactic survey : average broadband X-ray spectral properties of the NuSTAR-detected AGNs.', Astrophysical journal., 849 (1). p. 57.

Abstract

We present a study of the average X-ray spectral properties of the sources detected by the NuSTAR extragalactic survey, comprising observations of the E-CDFS, EGS and COSMOS fields. The sample includes 182 NuSTAR sources (64 detected at 8-24 keV), with 3-24 keV fluxes ranging between f3−24keV≈10−14 and 6×10−13 erg/cm2/s (f8−24keV≈3×10−14−3×10−13 erg/cm2/s) and redshifts of z=0.04−3.21. We produce composite spectra from the Chandra+NuSTAR data (E≈2−40 keV, rest frame) for all the sources with redshift identifications (95%) and investigate the intrinsic, average spectra of the sources, divided into broad-line (BL) and narrow-line (NL) AGN, and also in different bins of X-ray column density and luminosity. The average power-law photon index for the whole sample is Γ=1.65+0.03−0.03, flatter than Γ≈1.8 typically found for AGN. While the spectral slope of BL and X-ray unabsorbed AGN is consistent with typical values (Γ=1.79+0.01−0.01), a significant flattening is seen in NL AGN and heavily-absorbed sources (Γ=1.60+0.08−0.05 and Γ=1.38+0.12−0.12, respectively), likely due to the effect of absorption and to the contribution from Compton reflection to the high-energy flux (E>10 keV). We find that the typical reflection fraction in our spectra is R≈0.5 (for Γ=1.8), with a tentative indication of an increase of the reflection strength with column density. While there is no significant evidence for a dependence of the photon index with X-ray luminosity in our sample, we find that R decreases with luminosity, with relatively high levels of reflection (R≈1.2) for L10−40keV<1044 erg/s and R≈0.3 for L10−40keV>1044 erg/s AGN, assuming Γ=1.8.

Item Type:Article
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Status:Peer-reviewed
Publisher Web site:https://doi.org/10.3847/1538-4357/aa9115
Publisher statement:© 2017. The American Astronomical Society. All rights reserved.
Date accepted:02 October 2017
Date deposited:29 November 2017
Date of first online publication:31 October 2017
Date first made open access:29 November 2017

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