@article{bef2ffbcc1ef46f8855ca1e94d33a18f,
title = "The weak Fe fluorescence line and long-term X-ray evolution of the Compton-thick active galactic nucleus in NGC7674",
abstract = "We present NuSTAR X-ray observations of the active galactic nucleus (AGN) in NGC7674. 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-offAGN 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 longterm X-ray light curve of NGC7674 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-offAGN 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 (NH) of 3 × 1024 cm-2 at present, and yields an intrinsic 2-10 keV luminosity of (3-5) × 1043 erg s-1. Realistic uncertainties span the range of≈(1-13)×1043 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.",
author = "P. Gandhi and A. Annuar and Lansbury, {G. B.} and D. Stern and Alexander, {D. M.} and Bauer, {F. E.} and S. Bianchi and Boggs, {S. E.} and Boorman, {P. G.} and Brandt, {W. N.} and M. Brightman and Christensen, {F. E.} and A. Comastri and Craig, {W. W.} and {Del Moro}, A. and M. Elvis and M. Guainazzi and Hailey, {C. J.} and Harrison, {F. A.} and M. Koss and I. Lamperti and G. Malaguti and A. Masini and G. Matt and S. Puccetti and C. Ricci and E. Rivers and Walton, {D. J.} and Zhang, {W. W.}",
note = "Funding Information: 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 supportwith 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). Thiswork 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 FacilitiesCouncil (STFC) for support (grant reference ST/J003697/2).AC and AMacknowledge 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. Publisher Copyright: {\textcopyright} 2017 The Authors.",
year = "2017",
month = jun,
day = "1",
doi = "10.1093/mnras/stx357",
language = "English (US)",
volume = "467",
pages = "4606--4621",
journal = "Monthly Notices of the Royal Astronomical Society",
issn = "0035-8711",
publisher = "Oxford University Press",
number = "4",
}