Suzaku view of the swift/bat active galactic nuclei. I. Spectral analysis of six active galactic nuclei and evidence for two types of obscured population

Abstract

We present a systematic spectral analysis with Suzaku of six active galactic nuclei (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 fitted with a base model consisting of heavily absorbed (log N H > 23.5 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 Ueda etal.) with an extremely small scattered fraction (f scat < 0.5%) and strong reflection component (R = Ω/2π ≳ 0.8, where Ω is the solid angle of the reflector), and three "classical-type" ones with f scat > 0.5% and R ≲ 0.8. The spectral parameters suggest that the new type has an optically thick torus for Thomson scattering (N H ∼ 1025 cm-2) with a small opening angle θ ∼20° viewed in a rather face-on geometry, while the classical type has a thin torus (N H ∼ 1023-24 cm-2) with θ ≳ 30°. We infer that a significant number of new-type AGNs with an edge-on view are missing in the current all-sky hard X-ray surveys. © 2009. The American Astronomical Society. All rights reserved.