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

Journal Article · Wed Nov 01 04:00:00 EDT 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/AA9115· OSTI ID:22875627

Del Moro, A. ^[1]; Alexander, D. M.; Lansbury, G. B. ^[2]; Aird, J. A. ^[3]; Bauer, F. E. ^[4]; Civano, F.; Lanz, L. ^[5]; Mullaney, J. R. ^[6]; Ballantyne, D. R. ^[7]; Brandt, W. N. ^[8]; Comastri, A. ^[9]; Gandhi, P. ^[10]; Harrison, F. A. ^[11]; Luo, B. ^[12]; others, and

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1. Max-Planck-Institut für Extraterrestrische Physik (MPE), Giessenbachstrasse 1, D-85748 Garching (Germany)
2. Centre for Extragalactic Astronomy, Department of Physics, Durham University, South Road, Durham, DH1 3LE (United Kingdom)
3. Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge, CB3 0HA (United Kingdom)
4. Instituto de Astrofísica and Centro de Astroingeniería, Facultad de Física, Pontificia Universidad Católica de Chile, Casilla 306, Santiago 22 (Chile)
5. Department of Physics and Astronomy, Dartmouth College, 6127 Wilder Laboratory, Hanover, NH 03755 (United States)
6. Department of Physics and Astronomy, University of Sheffield, Sheffield, S3 7RH (United Kingdom)
7. Center for Relativistic Astrophysics, School of Physics, Georgia Institute of Technology, Atlanta, GA 30332 (United States)
8. Department of Astronomy and Astrophysics, 525 Davey Lab, The Pennsylvania State University, University Park, PA 16802 (United States)
9. INAF—Osservatorio Astronomico di Bologna, via Gobetti 93/3, I-40129 Bologna (Italy)
10. Department of Physics and Astronomy, Faculty of Physical Sciences and Engineering, University of Southampton, Southampton, SO17 1BJ (United Kingdom)
11. Cahill Center for Astrophysics, 1216 East California Boulevard, California Institute of Technology, Pasadena, CA 91125 (United States)
12. School of Astronomy and Space Science, Nanjing University, Nanjing 210093 (China)

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 f{sub 3--24keV}≈10{sup −14} and 6 × 10{sup −13} erg cm{sup −2} s{sup −1} (f{sub 8--24keV}≈3×10{sup −14}--3×10{sup −13} erg cm{sup −2} s{sup −1}) and redshifts in the range 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) 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 Γ=1.65{sub −0.03}{sup +0.03}, flatter than the Γ≈1.8 typically found for AGNs. While the spectral slope of BL and X-ray unabsorbed AGNs is consistent with the typical values (Γ=1.79{sub −0.01}{sup +0.01}), a significant flattening is seen in NL AGNs and heavily absorbed sources (Γ=1.60{sub −0.05}{sup +0.08} and Γ=1.38{sub −0.12}{sup +0.12}, respectively), likely due to the effect of absorption and to the contribution from the Compton reflection component 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 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 R decreases with luminosity, with relatively high levels of reflection (R≈1.2) for L{sub 10--40keV}<10{sup 44} erg s{sup −1} and R≈0.3 for L{sub 10--40keV}>10{sup 44} erg s{sup −1} AGNs, assuming a fixed spectral slope of Γ=1.8.

• OSTI ID: 22875627
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 1 Vol. 849; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ABSORPTION
DENSITY
GALAXY NUCLEI
KEV RANGE
LUMINOSITY
QUASARS
RED SHIFT
REFLECTION
SPECTRA
UNIVERSE
X-RAY GALAXIES