Axisymmetric Simulations of Pulsar Wind Nebulae with a New Central-Type Scheme for Relativistic MHD

A third-order shock-capturing numerical scheme for three-dimensional special relativistic magnetohydrodynamics (3-D RMHD) is presented. Due to the difficulties in developing exact or even approximate Riemann solvers in RMHD, a simple two-speed central-type solver that requires the knowledge of only the local fast magnetosonic velocities is employed. First results from axisymmetric simulations of Pulsar Wind Nebulae (PWNe) are finally presented. We show that when the wind magnetization is high enough, magnetic hoop stresses at work downstream of the termination shock are able to collimate a polar jet-like outflow, with velocities similar to those observed in the Crab and Vela Nebulae (v≈ 0.5-0.7c).