Probing the Disk–Jet Connection of the Radio Galaxy 3C 120 Observed with Suzaku

Broad line radio galaxies (BLRGs) are a rare type of radio-loud AGN, in whichthe broad optical permitted emission lines have been detected in addition tothe extended jet emission. Here we report on deep (40ksec x4) observations ofthe bright BLRG 3C~120 using Suzaku. The observations were spaced a week apart,and sample a range of continuum fluxes. An excellent broadband spectrum wasobtained over two decades of frequency (0.6 to 50 keV) within each 40 ksecexposure. We clearly resolved the iron K emission line complex, finding that itconsists of a narrow K_a core (sigma ~ 110 eV or an EW of 60 eV), a 6.9 keVline, and an underlying broad iron line. Our confirmation of the broad linecontrasts with the XMM-Newton observation in 2003, where the broad line was notrequired. The most natural interpretation of the broad line is iron K lineemission from a face-on accretion disk which is truncated at ~10 r_g. Above 10keV, a relatively weak Compton hump was detected (reflection fraction of R ~0.6), superposed on the primary X-ray continuum of Gamma ~ 1.75. Thanks to thegood photon statistics and low background of the Suzaku data, we clearlyconfirm the spectral evolution of 3C120, whereby the variability amplitudedecreases with increasing energy. More strikingly, we discovered that thevariability is caused by a steep power-law component of Gamma ~2.7, possiblyrelated to the non-thermal jet emission. We discuss our findings in the contextof similarities and differences between radio-loud/quiet objects.Comment: 19 pages, 17 figures, Accepted for publication in PAS