Long-Term, Continuous Monitoring of the Broad Line Radio Galaxies 3C 390.3 and 3C 120 With the Rossi X-Ray Timing Explorer

摘要

We present a study of the flux and spectral variability of the two broad-lineradio galaxies (BLRGs) 3C 390.3 and 3C 120, observed almost daily with RXTE fornearly two months each in 1996 and 1997, respectively. Our original motivationfor this study was to search for systematic differences between BLRGs and theirradio-quiet counterparts, the Seyfert galaxies, whose temporal and spectralbehavior is better studied. We find that both 3C 390.3 and 3C 120 are highlyvariable, but in a different way, and quantify this difference by means of astructure function analysis. 3C 390.3 is significantly more variable than 3C120, despite its jet larger inclination angle, implying either that the X-rayvariability is not dominated by the jet or that two different variabilityprocesses are simultaneously at work in 3C 390.3. We performed anenergy-selected and time-resolved analysis based on the fractional variabilityamplitude and found that the variability amplitude of both objects is stronglyanticorrelated with the energy. This last result, along with the correlatedchange of the photon index with the X-ray continuum flux, can be qualitativelyexplained within the scenario of thermal Comptonization, generally invoked forradio-quiet active galaxies. Moreover, the time-resolved and energy-selectedfractional variability analyses show a trend opposite to that observed injet-dominated AGN (blazars), suggesting only a minor contribution of the jet tothe X-ray properties of BLRGs. Time-averaged spectral analysis indicates thepresence of a strong, resolved iron line with centroid at 6.4 keV and a weakreflection component in both objects. The overall PCA+HEXTE spectra are bestfitted with the constant density ionization model of Ross & Fabian, but with amodest ionization parameter(abridged).