Signatures of the disk-jet coupling in the Broad-line Radio Quasar 4C+74.26

Abstract

Here we explore the disk-jet connection in the broad-line radio quasar 4C+74.26, utilizing the results of the 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 \(250 \pm 42\) 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 relativistic outflow. This scenario is supported by the re-analysis of the NuSTAR data, modelled in terms of a relativistic reflection from the disk illuminated by the coronal emission, which returns the inner disk radius \(R_{\rm in}/R_{\rm ISCO} =35^{+40}_{-16}\). We discuss the global energetics in the system, arguing that while the accretion proceeds at the Eddington rate, with the accretion-related bolometric luminosity \(L_{\rm bol} \sim 9 \times 10^{46}\) erg s\(^{-1}\) \(\sim 0.2 L_{\rm Edd}\), the jet total kinetic energy \(L_\textrm{j} \sim 4 \times 10^{44}\) erg s\(^{-1}\), inferred from the dynamical modelling of the giant radio lobes in the source, constitutes only a small fraction of the available accretion power.