SIMULATIONS OF RELATIVISTIC EXTRAGALACTIC JETS

We present the first results of axisymmetric jet simulations for both nonrelativistic and relativistic (gamma = 5 and 10) flow speeds, employing a relativistic hydrodynamic code which we have found to be both robust and efficient. We find the same gross morphology in all cases, but the relativistic runs exhibit little instability and less well-defined structure internal to the jet: this might explain the difference between (relatively slow) BL Lac objects and (faster) QSOs. We find that the choice of adiabatic index makes a small but discernible difference to the structure of the shocked jet and ambient media. Our code employs a solver of the Godunov type, with approximate solution of the local Riemann problems, applied to laboratory frame variables. Lorentz transformations provide the rest frame quantities needed for the estimation of wave speeds, etc. This is applied within the framework of an adaptive mesh refinement algorithm, allowing us to perform high-resolution, two-dimensional simulations with modest computing resources.