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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). Art. No. 57. ISSN 1538-4357. doi:10.3847/1538-4357/aa9115.

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We present a study of the average X-ray spectral properties of the sources detected by the NuSTARextragalactic 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_(3-24 kev) ≈ 10^(-14) and 6 × 10^(−13) erg cm^(−2) s^(−1) (f_(8-24 kev) ≈ 3 x 10^(-14)-3 x 10^(-13) erg cm^(−2) s^(−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^(+0.03)_(-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^(+0.01)_(-0.01)), a significant flattening is seen in NL AGNs 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 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_(10-40 kev) < 10^(44) erg s^(−1) and R ≈ 0.3 for L_(10-40 kev) > 10^(44) erg s^(−1) AGNs, assuming a fixed spectral slope of Γ = 1.8.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Alexander, D. M.0000-0002-5896-6313
Aird, J. A.0000-0003-1908-8463
Bauer, F. E.0000-0002-8686-8737
Civano, F.0000-0002-2115-1137
Mullaney, J. R.0000-0002-3126-6712
Ballantyne, D. R.0000-0001-8128-6976
Brandt, W. N.0000-0002-0167-2453
Comastri, A.0000-0003-3451-9970
Gandhi, P.0000-0003-3105-2615
Harrison, F. A.0000-0003-2992-8024
Lansbury, G. B.0000-0002-5328-9827
Lanz, L.0000-0002-3249-8224
Luo, B.0000-0002-9036-0063
Marchesi, S.0000-0001-5544-0749
Puccetti, S.0000-0002-2734-7835
Ricci, C.0000-0001-5231-2645
Saez, C.0000-0002-4933-7208
Stern, D.0000-0003-2686-9241
Treister, E.0000-0001-7568-6412
Zappacosta, L.0000-0002-4205-6884
Additional Information:© 2017 The American Astronomical Society. Received 2017 February 6; revised 2017 September 26; accepted 2017 October 2; published 2017 October 31. We thank A. Corral for useful discussions about the spectral averaging method presented in her work. A.D.M. thanks the financial support from the Max Plank Society and the UK Science and Technology Facilities Council (STFC, ST/L00075X/1, A.D.M. and D.M.A.; ST/K501979/1, G.B.L.). F.E.B. and E.T. acknowledge support from CONICYT-Chile (Basal-CATA PFB-06/2007, "EMBIGGEN" Anillo ACT1101, FONDECYT Regular 1141218 [F.E.B.] and 1160999 [E.T.]); F.E.B. also thanks the Ministry of Economy, Development, and Tourism's Millennium Science Initiative through grant IC120009, awarded to the Millennium Institute of Astrophysics (MAS). P.G. thanks the STFC for support (ST/J003697/2). W.N.B. acknowledges support from the Caltech NuSTAR subcontract 44A-1092750 and NASA ADP grant NNX10AC99G. A.C. and L.Z. acknowledge support from the ASI/INAF grant I/037/12/0 011/13. This work was supported under NASA contract no. NNG08FD60C and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by the National Aeronautics and Space Administration. We thank the NuSTAR Operations, Software, and Calibration teams for support with the execution and analysis of these observations. This research has made use of the NuSTAR Data Analysis Software (NuSTARDAS) jointly developed by the ASI Science Data Center (ASDC, Italy) and the California Institute of Technology (USA).
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Max Plank SocietyUNSPECIFIED
Science and Technology Facilities Council (STFC)ST/L00075X/1
Science and Technology Facilities Council (STFC)ST/K501979/1
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)Anillo ACT1101
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1160999
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Science and Technology Facilities Council (STFC)ST/J003697/2
Caltech NuSTAR subcontract44A-1092750
Agenzia Spaziale Italiana (ASI)I/037/12/0 011/13
Subject Keywords:galaxies: active – quasars: general – surveys – X-rays: galaxies
Issue or Number:1
Record Number:CaltechAUTHORS:20171031-103333243
Persistent URL:
Official Citation:A. Del Moro et al 2017 ApJ 849 57
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:82802
Deposited By: Tony Diaz
Deposited On:31 Oct 2017 17:54
Last Modified:28 Nov 2022 22:52

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