Helical jet in the gravitationally lensed blazar PKS1830-211

Abstract

Recent radio very long baseline interferometry observations of the complex gravitationally lensed system PKS 1830-211 have thrown up some questions with regard to the processes occurring at the heart of the blazar source at a redshift of 2.51, which is viewed almost straight down the jet axis. This work links, by a model of a helical jet tracked by ballistically ejected plasmons from a precessing nozzle, observations on the scale of tens of microarcseconds to those on the scale of milliarcseconds. An observed jet precession period of 1.08 yr is inferred from the model, translating to an intrinsic period of 30.8 yr for a source at redshift zs= 2.51 and an assumed jet bulk velocity β of 0.99c. This fits well with the picture of the active galactic nucleus hosting a binary black hole system at its centre, with the jet emitted by one member of the system and the precession as being a result of its orbital motion around its companion.