We used the PLUTO numerical code to perform 2D axisymmetric and full 3D resistive relativistic magnetohydrodynamic (MHD) simulations, employing spherical coordinates with spatial radial stretching. We considered and compared different models for physical resistivity, which must be small but still dominate over the intrinsic numerical dissipation (which yields unwanted smearing of structures in any ideal MHD code). All simulations were performed using an axisymmetric analytical model for both the jet propagation environment and the jet injection. As expected, no qualitative differences are detected due to the effect of finite conductivity, but significant quantitative differences in the jet structure and induced turbulence are clearly seen in 2D axisymmetric simulations. We see the formation of regions with a resistive electric field parallel to the magnetic field, and nonthermal particle acceleration may be enhanced there. The level of dissipated Ohmic power is also dependent on the various recipes for resistivity. Most of the differences arise before the breakout from the inner environment, whereas once the jet enters the external weakly magnetized environment region, these differences are preserved during further propagation despite the lower grid refinement. We also compared our 2D simulations with a fully three-dimensional run in order to assess the impact of the lack of axisymmetry on the jet propagation and evolution, and on the reconnection and dissipation processes.
We have performed the first systematic study of the propagation of astrophysical magnetized relativistic jets in the context of resistive relativistic magnetohydrodynamics (RRMHD) simulations. Simulations are obtained with the PLUTO code. The Taub equation of state is combined here for the first time with IMplicit-EXplicit Runge-Kutta routines for time-stepping, allowing a proper treatment of stiff terms in the evolutionary equation for the electric field. We investigated different values and models for the plasma resistivity coefficient, assessing their impact on the level of turbulence, the formation of current sheets and reconnection plasmoids, and the electromagnetic energy content. 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, results are very similar to ideal runs, where 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, preserving the development of turbulence and sharp current sheets, possible sites for the acceleration of the non-thermal particles producing the observed high-energy emission.
Diffusive shock acceleration has been pointed out as responsible for particle acceleration in astrophysical sources. Magnetic reconnection, the topological rearrangement of magnetic field lines in plasma, has often been invoked as a more efficient and universal acceleration process. We have combined the new module of the PLUTO code, which solves resistive relativistic magnetohydrodynamics equations, with the particle module of the PLUTO code, performing numerical simulations of test particle acceleration in relativistic magnetic reconnection sites using a hybrid particle-fluid code, showing that magnetic reconnection is a good candidate for particle acceleration in astrophysical sources. Dependence on magnetization, guide field, and resistivity has been studied, showing that magnetic reconnection is a more general and universal acceleration process than diffusive shock acceleration.