IC 3639—A NEW BONA FIDE COMPTON-THICK AGN UNVEILED BY NuSTAR

Abstract

We analyse 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 10 (L 2 -10 keV [erg s−1 ]) = 43.4 +0.6 −1.1 to 90% confidence, almost 400 times the observed flux, and consistent with various multi-wavelength diagnostics. Such a high intrinsic to observed flux ratio in addition to an Fe-Kα fluorescence line equivalent width exceeding 2 keV is extreme amongst known bona fide CTK AGN, which we suggest are both due to the high level of obscuration present around IC 3639. Our study demonstrates that broadband spectroscopic modelling with NuSTAR enables large corrections for obscuration to be carried out robustly, and emphasises the need for improved modelling of AGN tori showing intense iron fluorescence.

BAT AGN Spectroscopic Survey. V. X-Ray Properties of the Swift /BAT 70-month AGN Catalog

“…NuSTAR (Harrison et al 2013), launched in 2012, is the first on-orbit focusing hard X-ray telescope, and its serendipitous survey has detected 497 sources in the first 40 months of observations (Lansbury et al 2017b; see also Chen et al 2017). Thanks to its revolutionary characteristics, NuSTAR has been very efficient in constraining the properties of heavily obscured AGNs (e.g., Baloković et al 2014;Gandhi et al 2014;Stern et al 2014;Annuar et al 2015Annuar et al , 2017Brightman et al 2015;Koss et al 2015Koss et al , 2016bLansbury et al 2015Lansbury et al , 2017aBoorman et al 2016;Ricci et al 2016aRicci et al , 2016bRicci et al , 2017aRicci et al , 2017b. The recently launched mission AstroSat (Singh et al 2014) carries on board two hard X-ray instruments: the Large Area Xenon Proportional Counters (LAXPC; 3-80 keV) and the cadmiumzinc-telluride coded-mask imager (CZTI, 10-150 keV).…”

Embedded AGN and star formation in the central 80 pc of IC 3639

“…3), but requires that little or no dust emission at all should come from the innermost ∼ 0.4 pc. An inner radius of roughly half a parsec would imply a very high UV luminosity (∼ 7 × 10 45 erg s −1 ), which is significantly larger than the upper error limit of L disc < 1.3 × 10 45 erg s −1 given by Boorman et al (2016) at 90% confidence. The correlated flux predicted would overestimate the MIDI measurements if either a fainter luminosity is considered (corresponding to a smaller R in ), a more concentrated dust distribution is used (α < 0), or a temperature gradient index for large grains (β ∼ −0.5) is assumed.…”

“…Violet triangles correspond to the UV core. The grey-shaded area indicates the 2-10 keV and 0.5-30 keV intrinsic fluxes estimated for the models T and M in Boorman et al (2016).…”

“…We assume an inner torus radius of R in = 0.08 pc (from Suganuma et al 2006;Kishimoto et al 2007), corresponding to a nuclear UV luminosity of L UV ∼ 3×10 44 erg s −1 , which was derived from the L X ∼ 2×10 43 erg s −1 based on NuSTAR observations (from Boorman et al 2016, adapted to the distance used in this work) and the L UV -L X relation from Marchese et al (2012). We further assume a sublimation temperature of 1500 K, a grain size of 0.05 µm, and a dust temperature gradient index of β = −0.36, corresponding to ISM grains [T ∝ (r/R in ) β ; Barvainis 1987].…”

“…Its nucleus is strongly absorbed in X-rays (N H > 3.6 × 10 24 cm −2 , i.e. Compton-thick; Boorman et al 2016). In the UV, images from the Faint Object Camera (FOC) on board the Hubble Space Telescope (HST) reveal an extended morphology along the east-west axis (González Delgado et al 1998;see Fig.…”