Probing the disk-jet connection of the radio galaxy 3C 120 observed with Suzaku

Abstract

We report on deep (40 ks × 4) observations of the bright broad line radio galaxy 3C 120 using Suzaku. The observations were spaced one week apart, and sampled a range of continuum fluxes. An excellent broadband spectrum was obtained over two decades of frequency (0.6 to 50keV) within each 40 ks exposure. We clearly resolved the iron K emission-line complex, finding that it consists of a narrow Kα core (σ ≃ 110eV or an EW of 60 eV), a 6.9 keV line, and an underlying broad iron line. Our confirmation of the broad line contrasts with the XMM-Newton observation in 2003, where the broad line was not required. The most natural interpretation of the broad line is iron K line emission from a face-on accretion disk that is truncated at ∼ 10 r g. Above 10 keV, a relatively weak Compton hump was detected (reflection fraction of R ≃ 0.6), superposed on the primary X-ray continuum of Γ ≃ 1.75. Thanks to the good photon statistics and low background of the Suzaku data, we clearly confirm the spectral evolution of 3C 120, whereby the variability amplitude decreases with increasing energy. More strikingly, we discovered that the variability is caused by a steep power-law component of Γ ≃ 2.7, possibly related to non-thermal jet emission. We discuss our findings in the context of similarities and differences between radio-loud/quiet objects. © 2007. Astronomical Society of Japan.