Speaker
Description
Being the galactic cousins of jetted active galactic nuclei (AGN), microquasars in our Milky Way are important astrophysical systems to study jet physics. Recent IXPE observations of SS 433 revealed very high X-ray polarization degree in its e1 knot. The underlying magnetic field appears to be along the jet direction, suggesting a dominating poloidal magnetic field component in this area. However, given the very large size of the X-ray emission region, the derived poloidal magnetic flux would be much higher than that can be supplied by the central engine of SS 433. Here we present large-scale magnetohydrodynamic simulations of kinetic and magnetic jets, coupled with polarized radiation transfer. We find that in a magnetic jet, strong kink instabilities can twist local magnetic field lines, which can reproduce the high X-ray polarization degree that is observed by IXPE. The apparently dominating poloidal magnetic field component then originates from toroidal magnetic fields that are twisted by kink instabilities. On the other hand, if the magnetic energy and flux conversion happens much closer to the central engine, a kinetic jet can reproduce the IXPE observation via recollimation shocks. Very interestingly, these two models predict distinct polarization in the e2 knot of SS 433. Future IXPE observations of e2 will therefore distinguish the two jet scenarios.
