Relativistic Jet Response to Precession and Wave‐Wave Interactions

Three dimensional numerical simulations of the response of a Lorentz factor2.5 relativistic jet to precession at three different frequencies have beenperformed. Low, moderate and high precession frequencies have been chosenrelative to the maximally unstable frequency predicted by a Kelvin-Helmholtzstability analysis. Transverse motion and velocity decreases as the precessionfrequency increases. Although helical displacement of the jet decreases inamplitude as the precession frequency increases, a helical shock is generatedin the medium external to the jet at all precession frequencies. Complexpressure and velocity structure inside the jet is shown to be produced by acombination of the helical surface and first body modes predicted by a normalmode analysis of the relativistic hydrodynamic equations. The surface and firstbody mode have different wave speed and wavelength, are launched in phase bythe periodic precession, and exhibit beat patterns in synthetic emissionimages. Wave (pattern) speeds range from $0.41c$ to $0.86c$ but beat patternsremain stationary. Thus, we find a mechanism that can produce differentiallymoving and stationary features in the jet.Comment: 24 pages, 9 figures, figures in tex