SYNCHROTRON EMISSION FROM BENT SHOCKED RELATIVISTIC JETS .2. SHOCK-WAVES IN HELICAL JETS

We present multi-wavelength numerical results of a computer code, which solves the transfer equations for the synchrotron emission in compact extragalactic relativistic jets with bends and shock waves. We show those results for a rectilinear shocked jet and for a helicoidal shocked jet. The 'flare' in the total and polarized fluxes produced by the ejection of the shock wave from the core of the source appears earlier at higher frequencies, and later at lower frequencies as the flare develops. An anticorrelation, which turns later into a correlation, due to the dependence of the polarized flux on the opacity of the shocked flow, is observed between the time evolution of the total and polarized flux densities as the shock wave evolves along a jet. In the helical model, the strongest emission is obtained when the shock wave reaches the bent regions towards the observer, where the maximum Doppler boosting, the lengthening of the integration column, and the shock effects are simultaneously present and add to each other. The component associated with the shocked region has the electric vector parallel to the jet axis, due to the enhancement of the magnetic field parallel to the shock front. The simulations presented here show that the superluminal components observed in some VLBI maps can be associated with shock waves travelling along the jets.