Application of Clumpy Torus Model to Broadband X-ray Spectra of Two Seyfert 1 Galaxies: IC 4329A and NGC 7469

Abstract

We apply a new X-ray clumpy torus model called XCLUMPY (Tanimoto et al. 2019), where the clump distribution is assumed to be the same as in the infrared clumpy torus model (CLUMPY) by Nenkova et al. 2008, to the broadband X-ray spectra of type-1 active galactic nuclei (AGNs) for the first time. We analyze the archival data of IC 4329A and NGC 7469 observed with NuSTAR/Suzaku and NuSTAR/XMM-Newton, respectively, whose infrared spectra were studied with CLUMPY by Ichikawa et al. 2015 and optical extinctions ($A_{\rm V}$) of the tori were estimated. We consider two models, invoking (Model 1) a relativistic reflection component from the accretion disk and (Model 2) a partial absorber. Assuming that the narrow Fe K$α$ emission line at 6.4 keV originates from the torus, we separate the contribution of the torus reflection components in the total spectra. Our models yield equatorial hydrogen column densities of the tori to be $N^{\rm Equ}_{\rm H} =$ (0.53--1.43) $\times 10^{23}~\rm cm^{-2}$ and $N^{\rm Equ}_{\rm H} =$ (0.84--1.43) $\times 10^{24}~\rm cm^{-2}$, for IC 4329A and NGC 7469, respectively. We find that the $N_{\rm H}/A_{\rm V}$ ratios in the tori are by factors of 25--68 (IC 4329A) and 2.4--3.9 (NGC 7469) smaller than that in the Galactic interstellar medium (ISM). These results suggest that a non-negligible fraction of AGNs are 'dust-rich' compared with the Galactic ISM, as opposite to the general trend previously reported in many obscured AGNs.