Structure and Emission of Parsec-Scale Jets in Quasars

Abstract

The moving knots observed in VLBI of compact quasars are due to off-axis substructures in the parsec-scale jets which are dragged along by the underlying plasma flow. This is suggested by detailed MHD models for the structure of relativistic jets on the parsec–scale that are based on exact solutions of the nonlinear Grad–Schlüter–Shafranov equation in the asymptotic domain. These jet models are characterized by a current–carrying core and a current–free envelope. The corresponding core–radius Rc = upRL is related to the poloidal jet velocity up and the light cylinder radius RL generated by the rotation of the magnetic surfaces. The Poynting flux, which has an inhomogeneous distribution in the jet, provides an off–axis energy reservoir that could be tapped and converted into particle acceleration by non-axisymmetric instabilities in the core–jet structure. Evidence is presented that quasi-periodic synchrotron emission (in the IR–optical) and inverse Compton emission (in X– and γ–rays) from freshly accelerated electrons are due to a lighthouse effect of the rotating knots.