Suzaku View of the Swift/BAT Active Galactic Nuclei (I): Spectral Analysis of Six AGNs and Evidence for Two Types of Obscured Population

Abstract

We present a systematic spectral analysis with Suzaku of six AGNs detected in the Swift/BAT hard X-ray (15--200 keV) survey, Swift J0138.6-4001, J0255.2-0011, J0350.1-5019, J0505.7-2348, J0601.9-8636, and J1628.1-5145. This is considered to be a representative sample of new AGNs without X-ray spectral information before the BAT survey. We find that the 0.5--200 keV spectra of these sources can be uniformly fit with a base model consisting of heavily absorbed (log $N_{\rm{H}} > 23.5 \rm{cm}^{-2}$) transmitted components, scattered lights, a reflection component, and an iron-K emission line. There are two distinct groups, three "new type" AGNs (including the two sources reported by \citealt{Ueda2007}) with an extremely small scattered fraction ($f_{\rm{scat}} < 0.5$) and strong reflection component ($R = \Omega / 2 \pi \gtrsim 0.8$ where $\Omega$ is the solid angle of the reflector), and three "classical type" ones with $f_{\rm{scat}} > 0.5$ and $R \lesssim 0.8$. The spectral parameters suggest that the new type has an optically thick torus for Thomson scattering ($N_{\rm{H}} \sim 10^{25} \rm{cm}^{-2}$) with a small opening angle $\theta \sim 20^{\circ}$ viewed in a rather face-on geometry, while the classical type has a thin torus ($N_{\rm{H}} \sim 10^{23-24} \ \rm{cm}^{-2}$) with$\theta \gtrsim 30^{\circ}$. We infer that a significant number of new type AGNs with an edge-on view is missing in the current all-sky hard X-ray surveys.Comment: 11 pages, 6 figures, accepted for publication in The Astrophysical Journa