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the weak fe fluorescence line and long-term x-ray evolution of the compton-thick active galactic nucleus in ngc7674We 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-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 K(alpha) emission line (equivalent width [EW] of approximately 0.4 keV) and a strong Fe XXVI ionized line (EW approximately 0.2 keV).We construct an updated long-term X-ray light curve of NGC7674 and find that the observed 2-10 keV flux has remained constant for the past approximately 20 yr, following a high-flux state probed by Ginga. Light travel time arguments constrain the minimum radius of the reflector to be approximately 3.2 pc under the switched-off AGN scenario, approximately 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(sub H)) of 3 x 10(exp 24) cm(exp -2) at present, and yields an intrinsic 2-10 keV luminosity of (3-5) x 10(exp 43) erg s(exp -1). Realistic uncertainties span the range of approximately (1-13) x 10(exp 43) erg s1. 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 K line
Document ID
20170006108
Document Type
Reprint (Version printed in journal)
External Source(s)
Authors
Ghandi, P.
(Southampton Univ. Highfield, United Kingdom)
Annuar, A.
(Durham Univ. United Kingdom)
Lansbury, G. B.
(Durham Univ. United Kingdom)
Stern, D.
(Jet Propulsion Lab., California Inst. of Tech. Pasadena, CA, United States)
Alexander, D. M.
(Durham Univ. United Kingdom)
Bauer, F. E.
(Universidad Catolica de Chile Santiago, Chile)
Bianchi, S.
(Universita degli Studi Roma Tre Rome, Italy)
Boggs, S. E.
(California Univ. Berkeley, CA, United States)
Boorman, P. G.
(Southampton Univ. Highfield, United Kingdom)
Brandt, W. N.
(Pennsylvania State Univ. University Park, PA, United States)
Brightman, M.
(California Inst. of Tech. Pasadena, CA, United States)
Christensen, F. E.
(Technical Univ. of Denmark Lyngby, Denmark)
Comastri, A.
(Istituto Nazionale di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Bologna, Italy)
Craig, W. W.
(Technical Univ. of Denmark Lyngby, Denmark)
Del Moro, A.
(Max-Planck-Inst. fuer Extraterrestrische Physik Garching, Germany)
Elvis, M.
(Harvard-Smithsonian Center for Astrophysics Cambridge, MA, United States)
Guainazzi, M.
(Tokyo Univ. Sagamihara, Japan)
Hailey, C. J.
(Columbia Univ. New York, NY, United States)
Harrison, F. A.
(California Inst. of Tech. Pasadena, CA, United States)
Koss, M.
(Eidgenoessische Technische Hochschule Zurich, Switzerland)
Lamperti, I.
(Eidgenoessische Technische Hochschule Zurich, Switzerland)
Malaguti, G.
(Istituto Nazionale di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Bologna, Italy)
Masini, A.
(Istituto Nazionale di Astrofisica Spaziale e Fisica Cosmica (INAF-IASF) Bologna, Italy)
Matt, G.
(Universita degli Studi Roma Tre Rome, Italy)
Puccetti, S.
(Universita degli Studi Roma Tre Rome, Italy)
Ricci, C.
(Universidad Catolica de Chile Santiago, Chile)
Rivers, E.
(California Inst. of Tech. Pasadena, CA, United States)
Walton, D. J.
(Cambridge Univ. Cambridge, United Kingdom)
Zhang, William W.
(NASA Goddard Space Flight Center Greenbelt, MD United States)
Date Acquired
July 6, 2017
Publication Date
February 13, 2017
Publication Information
Publication: Monthly Notices of the Royal Astronomical Society
Volume: 467
Issue: 4
ISSN: 0035-8711
Subject Category
Astrophysics
Report/Patent Number
GSFC-E-DAA-TN44020
Funding Number(s)
CONTRACT_GRANT: ST/K501979/1
CONTRACT_GRANT: NNX15AV27G
CONTRACT_GRANT: IC120009
CONTRACT_GRANT: ST/J003697/2
CONTRACT_GRANT: ST/I0015731/1
CONTRACT_GRANT: ASI-INAFI/037/12/0
CONTRACT_GRANT: I/037/12/0-011/13
Distribution Limits
Public
Copyright
Other
Keywords
galaxies: Seyfert –X-rays: individual (NGC 7674).