Relativistic jet response to precession and wave-wave interactions

Three-dimensional numerical simulations of the response of a Lorentz factor 2.5 relativistic jet to precession at three different frequencies have bee n performed. Low-, moderate-, and high-precession frequencies have been cho sen relative to the maximally unstable frequency predicted by a Kelvin-Helm holtz stability analysis. The transverse motion and velocity decreases as t he precession frequency increases. Although the helical displacement of the jet decreases in amplitude as the precession frequency increases, a helica l shock is generated in the medium external to the jet at all precession fr equencies. Complex pressure and velocity structure inside the jet are shown to be produced by a combination of the helical surface and first-body mode s predicted by a normal mode analysis of the relativistic hydrodynamic equa tions. The surface and first-body modes have different wave speeds and wave lengths, are launched in phase by the periodic precession, and exhibit beat patterns in synthetic emission images. Wave (pattern) speeds range from 0. 41c to 0.86c, but the beat patterns remain stationary. Thus, we find a mech anism that can produce differentially moving and stationary features in the jet.