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

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

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


Authors

A. Del Moro

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. Treister

L. Zappacosta



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.

Citation

Del Moro, A., Alexander, D., Aird, J., Bauer, F., Civano, F., Mullaney, J., …Zappacosta, L. (2017). The NuSTAR Extragalactic Survey: Average Broadband X-Ray Spectral Properties of the NuSTAR-detected AGNs. Astrophysical Journal, 849(1), Article 57. https://doi.org/10.3847/1538-4357/aa9115

Journal Article Type Article
Acceptance Date Oct 2, 2017
Online Publication Date Oct 31, 2017
Publication Date Oct 31, 2017
Deposit Date Nov 29, 2017
Publicly Available Date Nov 29, 2017
Journal Astrophysical Journal
Print ISSN 0004-637X
Publisher American Astronomical Society
Peer Reviewed Peer Reviewed
Volume 849
Issue 1
Article Number 57
DOI https://doi.org/10.3847/1538-4357/aa9115

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Copyright Statement
© 2017. The American Astronomical Society. All rights reserved.





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