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IC 3639 - a new bona fide Compton-thick AGN unveiled by NuSTAR.

Boorman, P.G. and Gandhi, P. and Alexander, D.M. and Annuar, A. and Ballantyne, D.R. and Bauer, F. and Boggs, S.E. and Brandt, W.N. and Brightman, M. and Christensen, F.E. and Craig, W.W. and Farrah, D. and Hailey, C.J. and Harrison, F.A. and Hönig, S.F. and Koss, M.J. and LaMassa, S.M. and Massini, A. and Ricci, C. and Risaliti, G. and Stern, D. and Zhang, W. (2016) 'IC 3639 - a new bona fide Compton-thick AGN unveiled by NuSTAR.', Astrophysical Journal, 833 (2). pp. 245-262.


We analyze high-quality NuSTAR observations of the local (z = 0.011) Seyfert 2 active galactic nucleus (AGN) IC 3639, in conjunction with archival Suzaku and Chandra data. This provides the first broadband X-ray spectral analysis of the source, spanning nearly two decades in energy (0.5–30 keV). Previous X-ray observations of the source below 10 keV indicated strong reflection/obscuration on the basis of a pronounced iron fluorescence line at 6.4 keV. The hard X-ray energy coverage of NuSTAR, together with self-consistent toroidal reprocessing models, enables direct broadband constraints on the obscuring column density of the source. We find the source to be heavily Compton-thick (CTK) with an obscuring column in excess of 3.6 10 ´ 24 cm−2 , unconstrained at the upper end. We further find an intrinsic 2–10 keV luminosity of - = - + log erg s 43.4 L 10 2 10 keV 1 1.1 0.6 ( [ ]) – to 90% confidence, almost 400 times the observed flux, and consistent with various multiwavelength diagnostics. Such a high ratio of intrinsic to observed flux, in addition to an Fe-Kα fluorescence line equivalent width exceeding 2 keV, is extreme among known bona fide CTK AGNs, which we suggest are both due to the high level of obscuration present around IC 3639. Our study demonstrates that broadband spectroscopic modeling with NuSTAR enables large corrections for obscuration to be carried out robustly and emphasizes the need for improved modeling of AGN tori showing intense iron fluorescence.

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Publisher statement:© 2016. The American Astronomical Society. All rights reserved.
Date accepted:26 October 2016
Date deposited:26 January 2017
Date of first online publication:20 December 2016
Date first made open access:26 January 2017

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