The XMM-Newton view of the broad-line radio galaxy 3C 120

We present the results of a 127-ks XMM-Newton observation of the broad-line radio galaxy 3C 120 performed simultaneously with RXTE. The data have yielded the highest quality 0.6-10 keV spectrum of a radio-loud active galaxy ever produced. The time-averaged spectrum is Seyfert-like, with a reflection amplitude R~ 0.5, and a neutral Fe Kα line with equivalent width ~53 eV. The line is slightly broadened with a FWHM ~ 10⁴ km s^-1. This is consistent with arising from an accretion disc radius of >~75 GM/c² at an inclination angle of ~10°, consistent with the limit of <14° derived from the radio jets. At low energies the spectrum requires excess absorption above the Galactic value and a soft excess that is best fitted with a bremsstrahlung model (kT= 0.3-0.4 keV). The total luminosity in the bremsstrahlung component is just under half of the total hard X-ray luminosity. The emission may originate in either the broad-line region, or in giant HII regions adjacent to the nucleus. Weak OVII and OVIII edges are detected with high precision, suggesting the presence of a warm absorber component. Broad-band 0.6-50 keV fits to the data cannot unambiguously determine the accretion mode in 3C 120. A two-component ionized disc model, with a very highly ionized reflector presumably arising from very close to the black hole, is only a small improvement over a truncated disc model. The strength of the soft X-ray emission features produced by the distant neutral reflector are overpredicted in our solar abundance model, implying that the heavy metal abundance in 3C 120 is subsolar. Both broad-band models could also fit a much shorter archival XMM-Newton observation. The total count rate declined by 20 per cent over the course of the long observation, while small-scale rapid variability was present at the level of a few per cent. A possible increase in the Fe Kα line flux, significant at the 90 per cent level, was identified at ~80 ks in the observation. The total unabsorbed luminosity of 3C 120 implies that it is accreting close to its Eddington rate, consistent with a model of a highly ionized thick disc. A possible connection between accretion disc thickness and radio jet production is discussed.