3D RMHD simulations of jet-wind interactions in high-mass X-ray binaries

Abstract

Context. Relativistic jets are ubiquitous in the Universe. In microquasars, especially in high-mass X-ray binaries, the interaction of jets with the strong winds driven by the massive and hot companion star in the vicinity of the compact object is fundamental for understanding the jet dynamics, nonthermal emission, and long-term stability. However, the role of the jet magnetic field in this process is unclear. In particular, it is still debated whether the magnetic field favors jet collimation or triggers more instabilities that can jeopardize the jet evolution outside the binary. Aims. We study the dynamical role of weak and moderate to strong toroidal magnetic fields during the first several hundred seconds of jet propagation through the stellar wind, focusing on the magnetized flow dynamics and the mechanisms of energy conversion. Methods. We developed the code Lóstrego v1.0, a new 3D relativistic magnetohydrodynamics code to simulate astrophysical plasmas in Cartesian coordinates. Using this tool, we performed the first 3D relativistic magnetohydrodynamics numerical simulations of relativistic magnetized jets propagating through the clumpy stellar wind in a high-mass X-ray binary. To highlight the effect of the magnetic field in the jet dynamics, we compared the results of our analysis with those of previous hydrodynamical simulations. Results. The overall morphology and dynamics of weakly magnetized jet models is similar to previous hydrodynamical simulations, where the jet head generates a strong shock in the ambient medium and the initial overpressure with respect to the stellar wind drives one or more recollimation shocks. On the timescales of our simulations (i.e., t < 200 s), these jets are ballistic and seem to be more stable against internal instabilities than jets with the same power in the absence of fields. However, moderate to strong toroidal magnetic fields favor the development of current-driven instabilities and the disruption of the jet within the binary. A detailed analysis of the energy distribution in the relativistic outflow and the ambient medium reveals that magnetic and internal energies can both contribute to the effective acceleration of the jet. Moreover, we verified that the jet feedback into the ambient medium is highly dependent on the jet energy distribution at injection, where hotter, more diluted and/or more magnetized jets are more efficient. This was anticipated by feedback studies in the case of jets in active galaxies.