Signatures of the Disk–Jet Coupling in the Broad-line Radio Quasar 4C+74.26

Abstract

We explore the disk–jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of multiwavelength monitoring of the source. The target is unique in that its radiative output at radio wavelengths is dominated by a moderately beamed nuclear jet, at optical frequencies by the accretion disk, and in the hard X-ray range by the disk corona. Our analysis reveals a correlation (local and global significance of 96% and 98% respectively) between the optical and radio bands, with the disk lagging behind the jet by 250 ± 42 days. We discuss the possible explanation for this, speculating that the observed disk and the jet flux changes are generated by magnetic fluctuations originating within the innermost parts of a truncated disk, and that the lag is related to a delayed radiative response of the disk when compared with the propagation timescale of magnetic perturbations along a relativistic outflow. This scenario is supported by re-analysis of NuSTAR data, modeled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns an inner disk radius . We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity L bol  ∼ 9 × 10 46 erg s −1  ∼ 0.2 L Edd , the jet total kinetic energy L j  ∼ 4 × 10 44 erg s −1 , inferred from the dynamical modeling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.