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The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC 7674

Gandhi, P. and Annuar, A. and Lansbury, G. B. and Stern, D. and Alexander, D. M. and Bauer, F. E. and Bianchi, S. and Boggs, S. E. and Boorman, P. G. and Brandt, W. N. and Brightman, M. and Christensen, F. E. and Comastri, A. and Craig, W. W. and Del Moro, A. and Elvis, M. and Guainazzi, M. and Hailey, C. J. and Harrison, F. A. and Koss, M. and Lamperti, I. and Malaguti, G. and Masini, A. and Matt, G. and Puccetti, S. and Ricci, C. and Rivers, E. and Walton, D. J. and Zhang, W. W. (2017) The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC 7674. Monthly Notices of the Royal Astronomical Society, 467 (4). pp. 4606-4621. ISSN 0035-8711.

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We present NuSTAR X-ray observations of the active galactic nucleus (AGN) in NGC 7674. The source shows a flat X-ray spectrum, suggesting that it is obscured by Compton-thick gas columns. Based upon long-term flux dimming, previous work suggested the alternate possibility that the source is a recently switched-off AGN with the observed X-rays being the lagged echo from the torus. Our high-quality data show the source to be reflection-dominated in hard X-rays, but with a relatively weak neutral Fe Kα emission line (equivalent width [EW] of ≈ 0.4 keV) and a strong Fe xxvi ionized line (EW ≈ 0.2 keV). We construct an updated long-term X-ray light curve of NGC 7674 and find that the observed 2–10 keV flux has remained constant for the past ≈ 20 yr, following a high-flux state probed by Ginga. Light travel time arguments constrain the minimum radius of the reflector to be ∼ 3.2 pc under the switched-off AGN scenario, ≈ 30 times larger than the expected dust sublimation radius, rendering this possibility unlikely. A patchy Compton-thick AGN (CTAGN) solution is plausible, requiring a minimum line-of-sight column density (N_H) of 3 × 10^(24) cm^(−2) at present, and yields an intrinsic 2–10 keV luminosity of (3–5) × 10^(43) erg s^(−1). Realistic uncertainties span the range of ≈ (1–13) × 10^(43) erg s^(−1). The source has one of the weakest fluorescence lines amongst bona fide CTAGN, and is potentially a local analogue of bolometrically luminous systems showing complex neutral and ionized Fe emission. It exemplifies the difficulty of identification and proper characterization of distant CTAGN based on the strength of the neutral Fe Kα line.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Gandhi, P.0000-0003-3105-2615
Annuar, A.0000-0003-0387-1429
Lansbury, G. B.0000-0002-5328-9827
Stern, D.0000-0003-2686-9241
Alexander, D. M.0000-0002-5896-6313
Bauer, F. E.0000-0002-8686-8737
Bianchi, S.0000-0002-4622-4240
Boggs, S. E.0000-0001-9567-4224
Boorman, P. G.0000-0001-9379-4716
Brandt, W. N.0000-0002-0167-2453
Brightman, M.0000-0002-8147-2602
Christensen, F. E.0000-0001-5679-1946
Comastri, A.0000-0003-3451-9970
Harrison, F. A.0000-0003-2992-8024
Koss, M.0000-0002-7998-9581
Lamperti, I.0000-0003-3336-5498
Masini, A.0000-0002-7100-9366
Matt, G.0000-0002-2152-0916
Puccetti, S.0000-0002-2734-7835
Ricci, C.0000-0001-5231-2645
Walton, D. J.0000-0001-5819-3552
Zhang, W. W.0000-0002-1426-9698
Alternate Title:The weak neutral Fe fluorescence line and long-term X-ray evolution of the Compton-thick AGN in NGC 7674
Additional Information:© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 February 8. Received 2017 February 7; in original form 2016 May 24. Published: 13 February 2017. This research has 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). This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester (Evans et al. 2009). PG thanks the Science and Technology Facilities Council (STFC) for support (grant reference ST/J003697/2). AC and AM acknowledge support from the ASI/INAF grant I/037/12/0-011/13. AC acknowledges the Caltech Kingsley visitor programme. We acknowledge financial support from Majlis Amanah Rakyat (MARA) Malaysia (AA), STFC grants ST/I0015731/1 (DMA) and ST/K501979/1 (GBL). WNB acknowledges California Institute of Technology (Caltech) NuSTAR subcontract 44A-1092750. SB acknowledges financial contribution from the agreement ASI-INAF I/037/12/0. We also acknowledge NASA NuSTAR A01 Award NNX15AV27G (FEB), CONICYT-Chile grants Basal-CATA PFB-06/2007 (FEB, CR), FONDECYT Regular 1141218 (FEB, CR), ‘EMBIGGEN’ Anillo ACT1101 (FEB, CR) and the Ministry of Economy, Development, and Tourism’s Millennium Science Initiative through grant IC120009, awarded to The Millennium Institute of Astrophysics, MAS (FEB). We thank the referee for detailed comments that helped us to make the presentation of results clearer and to place the discussion on a more robust footing.
Group:NuSTAR, Space Radiation Laboratory, Astronomy Department
Funding AgencyGrant Number
Science and Technology Facilities Council (STFC)ST/J003697/2
Agenzia Spaziale Italiana (ASI)I/037/12/0-011/13
Caltech Kingsley Visitor ProgramUNSPECIFIED
Majlis Amanah Rakyat (MARA)UNSPECIFIED
Science and Technology Facilities Council (STFC)ST/I0015731/1
Science and Technology Facilities Council (STFC)ST/K501979/1
Caltech NuSTAR subcontract44A-1092750
Agenzia Spaziale Italiana (ASI)I/037/12/0
Fondo Nacional de Desarrollo Científico y Tecnológico (FONDECYT)1141218
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)Anillo ACT1101
Iniciativa Científica Milenio del Ministerio de Economía, Fomento y TurismoIC120009
Issue or Number:4
Record Number:CaltechAUTHORS:20170428-150646304
Persistent URL:
Official Citation:P. Gandhi, A. Annuar, G. B. Lansbury, D. Stern, D. M. Alexander, F. E. Bauer, S. Bianchi, S. E. Boggs, P. G. Boorman, W. N. Brandt, M. Brightman, F. E. Christensen, A. Comastri, W. W. Craig, A. Del Moro, M. Elvis, M. Guainazzi, C. J. Hailey, F. A. Harrison, M. Koss, I. Lamperti, G. Malaguti, A. Masini, G. Matt, S. Puccetti, C. Ricci, E. Rivers, D. J. Walton, W. W. Zhang; The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC 7674. Mon Not R Astron Soc 2017; 467 (4): 4606-4621. doi: 10.1093/mnras/stx357
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:77068
Deposited By: Tony Diaz
Deposited On:28 Apr 2017 23:43
Last Modified:09 Mar 2020 13:19

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