Numerical simulations of a restarting jet

The first self-consistent two-dimensional numerical simulation of an axisymmetric intermittent jet is presented. It is found that if the jet parameters at the jet nozzle do not vary widely from one duty cycle to the next, the restarted jet will always be overdense if the original jet is underdense relative to the quiescent intergalactic medium. Although the working surface advance speed of the restarted jet is greater than that of the original jet, the Mach number of the advance speed is less. Because the advance speed Mach number of the new working surface is relatively low, the bow shock excited by the new jet is weak regardless of the strength of the original bow shock in the quiescent ambient medium. Because the bow shock and terminal Mach disk must have comparable strengths, the brightness contrast of emission features associated with the shock should be roughly the same. Without the momentum flux of the jet, the hot spot expands in a time short compared with the duty cycle. 27 refs