Radio emission from three-dimensional relativistic hydrodynamic jets: Observational evidence of jet stratification

We present the first radio emission simulations from high-resolution three- dimensional relativistic hydrodynamic jets; these simulations allow us to s tudy the observational implications of the interaction between the jet and the external medium. This interaction gives rise to a stratification of the jet in which a fast spine is surrounded by a slow high-energy shear layer. The stratification (in particular, the large specific internal energy and slow flow in the shear layer) largely determines the emission from the jet. If the magnetic field in the shear layer becomes helical (e.g., resulting from an initial toroidal field and an aligned field component generated by shear), the emission shows a cross section asymmetry, in which either the t op or the bottom of the jet dominates the emission. This, as well as limb o r spine brightening, is a function of the viewing angle and flow velocity, and the top/ bottom jet emission predominance can be reversed if the jet ch anges direction with respect to the observer or if it presents a change in velocity. The asymmetry is more prominent in the polarized flux because of field cancellation (Or amplification) along the line of sight. Recent obser vations of jet cross section emission asymmetries in the blazar 1055+018 ca n be explained by assuming the existence of a shear layer with a helical ma gnetic field.