Resistive relativistic MHD simulations of astrophysical jets

Abstract

Aims. The main goal of the present paper is to provide the first systematic numerical study of the propagation of astrophysical relativistic jets, in the context of high-resolution, shock-capturing Resistive Relativistic MagnetoHydroDynamic (RRMHD) simulations. We aim to investigate different values and models for the plasma resistivity coefficient, and to assess their impact on the level of turbulence, the formation of current sheets and reconnection plasmoids, the electromagnetic energy content, and the dissipated power. Methods. We used the PLUTO code for simulations and we assumed an axisymmetric setup for the jets, endowed with both poloidal and toroidal magnetic fields, and propagating in a uniform magnetized medium. The gas was assumed to be characterized by a realistic, Synge-like equation of state (the Taub equation), appropriate for such astrophysical jets. The Taub equation was combined here for the first time with the implicit-explicit Runge-Kutta time-stepping procedure, as required in RRMHD simulations. Results. The main result is that turbulence is clearly suppressed for the highest values of resistivity (low Lundquist numbers), current sheets are broader, and plasmoids are barely present, while for low values of resistivity the results are very similar to ideal runs, in which dissipation is purely numerical. We find that recipes employing a variable resistivity based on the advection of a jet tracer or on the assumption of a uniform Lundquist number improve on the use of a constant coefficient and are probably more realistic possible sites for the acceleration of the nonthermal particles that produce the observed high-energy emission, preserving as they do the development of turbulence and of sharp current sheets.