The termination region of high-mass microquasar jets

Abstract: The environment of high-mass X-ray binaries can be characterized either by the SNR that forms these systems, or by the wind from the companion massive star. These regions should be tenuous but very hot, and surrounded by a dense and cold shocked ISM shell. The interaction between the jet and such a complex medium, also affected by the system proper motion, can lead to very different jet termination structures. The evolution of the jet termination regions during the life of a high-mass microquasar is simulated to improve the present understanding of these structures. Also, the evolving emission characteristics are modeled to inform potential observational campaigns for this class of object. We have performed 2D numerical simulations of jets propagating in different scenarios, corresponding to different epochs after the formation of the high-mass X-ray binary, using the code Ratpenat. We have also made simple estimates of the non-thermal emission that could be produced in the jet termination regions. We find that, in the way through the hot and tenuous medium of the shocked wind/SNR ejecta, the jet suffers recollimation shocks in which it loses part of its thrust and ends in a strong shock inflating a hot cocoon. The jet head propagates with a speed similar to the medium sound speed, until it eventually reaches the denser and colder shocked ISM and the unperturbed ISM later on. In these last stages of evolution, the jet is significantly slowed down and can be disrupted. For relatively old sources, the microquasar peculiar velocity becomes important, leading to complete jet destruction. Extended non-thermal radiation can be generated in the jet termination regions, being hard X-rays and TeV photons the best suited wavelengths to observe these structures.