Recollimation Shocks in Magnetized Relativistic Jets

TL;DR

This study uses 2D relativistic magnetohydrodynamic simulations to explore how different magnetic field configurations affect shock structures in over-pressured jets, revealing significant impacts on jet dynamics and potential observable features.

Contribution

It provides a detailed analysis of how axial, toroidal, and helical magnetic fields influence recollimation shocks in relativistic jets, highlighting the magnetic topology's role in jet behavior.

Findings

Axial magnetic fields strengthen shocks and increase jet boost quadratically.

Toroidal fields weaken shocks and reduce jet boost systematically.

Helical fields produce complex shock structures depending on magnetic pitch.

Abstract

We have performed two-dimensional special-relativistic magnetohydrodynamic simulations of non-equilibrium over-pressured relativistic jets in cylindrical geometry. Multiple stationary recollimation shock and rarefaction structures are produced along the jet by the nonlinear interaction of shocks and rarefaction waves excited at the interface between the jet and the surrounding ambient medium. Although initially the jet is kinematically dominated, we have considered axial, toroidal and helical magnetic fields to investigate the effects of different magnetic-field topologies and strengths on the recollimation structures. We find that an axial field introduces a larger effective gas-pressure and leads to stronger recollimation shocks and rarefactions, resulting in larger flow variations. The jet boost grows quadratically with the initial magnetic field. On the other hand, a toroidal field leads to weaker recollimation shocks and rarefactions, modifying significantly the jet structure after the first recollimation rarefaction and shock. The jet boost decreases systematically. For a helical field, instead, the behaviour depends on the magnetic pitch, with a phenomenology that ranges between the one seen for axial and toroidal magnetic fields, respectively. In general, however, a helical magnetic field yields a more complex shock and rarefaction substructure close to the inlet that significantly modifies the jet structure. The differences in shock structure resulting from different field configurations and strengths may have observable consequences for disturbances propagating through a stationary recollimation shock.