SUZAKU OBSERVATIONS OF MODERATELY OBSCURED (COMPTON-THIN) ACTIVE GALACTIC NUCLEI SELECTED BY SWIFT/BAT HARD X-RAY SURVEY

Abstract

We report the results obtained by a systematic, broadband (0.5–150 keV) X-ray spectral analysis of moderately obscured (Compton-thin, 22 ≤ log N H < 24 ) active galactic nuclei (AGNs) observed with Suzaku and Swift /Burst Alert Telescope (BAT). Our sample consists of 45 local AGNs at z < 0.1 with log L 14 − 195 keV > 42 detected in the Swift /BAT 70-month survey, whose Suzaku archival data are available as of 2015 December. All spectra are uniformly fit with a baseline model composed of an absorbed cutoff power-law component, reflected emission accompanied by a narrow fluorescent iron-K α line from cold matter (torus), and scattered emission. The main results based on the above analysis are as follows. (1) The photon index is correlated with Eddington ratio, but not with luminosity or black hole mass. (2) The ratio of the luminosity of the iron-K α line to the X-ray luminosity an indicator of the covering fraction of the torus, shows significant anticorrelation with luminosity. (3) The averaged reflection strength derived from stacked spectra above 14 keV is larger in less luminous ( log L 10 − 50 keV ≤ 43.3 , R = 1.04 − 0.19 + 0.17 ) or highly obscured ( log N H > 23 , R = 1.03 − 0.17 + 0.15 ) AGNs than in more luminous ( log L 10 − 50 keV > 43.3 , R = 0.46 − 0.09 + 0.08 ) or lightly obscured ( log N H ≤ 23 , R = 0.59 − 0.10 + 0.09 ) objects. (4) The ratio of the luminosity of the [ O IV ] 25.89 μ m line to the X-ray luminosity is significantly smaller in AGNs with lower soft X-ray scattering fractions, suggesting that the former luminosity underestimates the intrinsic power of an AGN buried in a torus of small opening angle.