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P.E. Hardee (U. Alabama), P.A. Hughes (U. Michigan), A. Rosen (Armagh Obs.), E. Gomez (U. Alabama)
Three dimensional numerical simulations of the response of a 0.916c relativistic jet to three different precession frequencies have been performed. Low, moderate and high precession frequencies have been chosen relative to the maximally unstable frequency predicted by a Kelvin-Helmholtz stability analysis. Transverse motion and velocity decreases as the precession frequency increases. Although helical displacement of the jet decreases in amplitude as the precession frequency increases, a significant spiral pressure wave is generated in the medium external to the jet at all precession frequencies. Complex pressure and velocity structure inside the jet is shown to be produced by a combination of the helical surface and first body modes predicted by a normal mode analysis of the relativistic hydrodynamic equations. The surface and first body modes have different wave speed and wavelength, are launched in phase by the periodic precession, and exhibit beat patterns in synthetic emission images. Wave (pattern) speeds range from 0.62c to 0.86c but beat patterns remain stationary. Thus, we find a mechanism that can produce moving and stationary features in the jet.
P. Hardee, A. Rosen and E. Gomez acknowledge support from the National Science Foundation through grant AST-9802955 to the University of Alabama. P. Hughes acknowledges support from the National Science Foundation through grant AST-9617032 to the University of Michigan.