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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

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

Author(s) from Durham


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
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.