The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs

A. Del Moro, D. M. Alexander, J. A. Aird, F. E. Bauer, F. Civano, J. R. Mullaney, D. R. Ballantyne, W. N. Brandt, A. Comastri, P. Gandhi, F. A. Harrison, G. B. Lansbury, L. Lanz, B. Luo, S. Marchesi, S. Puccetti, C. Ricci, C. Saez, D. Stern, E. TreisterL. Zappacosta

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19 Scopus citations


We present a study of the average X-ray spectral properties of the sources detected by the NuSTAR extragalactic survey, comprising observations of the Extended Chandra Deep Field South (E-CDFS), Extended Groth Strip (EGS), and the Cosmic Evolution Survey (COSMOS). The sample includes 182 NuSTAR sources (64 detected at 8-24 keV), with 3-24 keV fluxes ranging between and 6 10-13 erg cm-2 s-1 (erg cm-2 s-1) and redshifts in the range of We produce composite spectra from the Chandra + NuSTAR data (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) active galactic nuclei (AGNs), and also in different bins of X-ray column density and luminosity. The average power-law photon index for the whole sample is, flatter than the typically found for AGNs. While the spectral slope of BL and X-ray unabsorbed AGNs is consistent with the typical values a significant flattening is seen in NL AGNs and heavily absorbed sources (and , respectively), likely due to the effect of absorption and to the contribution from the Compton reflection component to the high-energy flux ( keV). We find that the typical reflection fraction in our spectra is (for), with a tentative indication of an increase of the reflection strength with X-ray column density. While there is no significant evidence for a dependence of the photon index on X-ray luminosity in our sample, we find that decreases with luminosity, with relatively high levels of reflection for erg s-1 and for erg s-1 AGNs, assuming a fixed spectral slope of .

Original languageEnglish (US)
Article number57
JournalAstrophysical Journal
Issue number1
StatePublished - Nov 1 2017

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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