Large-scale Cavities Surrounding Microquasars Inferred from Evolution of Their Relativistic Jets

The black hole (BH) X-ray transient XTE J1550 - 564 has undergone a strong outburst in 1998 and two relativistic X-ray jets have been detected years later with the Chandra X-ray observatory; the eastern jet was found previously to have decelerated after its first detection. Here, we report a full analysis of the evolution of the western jet; significant deceleration is also detected in the western side. Our analysis indicates that there is a cavity outside the central source and the jets first traveled with constant velocity and then were slowed down by the interactions between the jets and the interstellar medium. The best-fitted radius of the cavity is ~0.31 pc on the eastern side and ~0.44 pc on the western side, and the densities also show asymmetry, of ~0.034 cm^-3 on the east to ~0.12 cm^-3 on the west. The best-fitted magnetic fields on both sides are ~0.5 mG. Similar analysis is also applied to another microquasar system, H 1743 - 322, and a large-scale low-density region is also found. Based on these results and the comparison with other microquasar systems, we suggest a generic scenario for microquasar jets, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them. We also suggest that either continuous jets or accretion disk winds, or both may be responsible for creating these cavities. Therefore X-ray jets from microquasars provide us with a promising method of probing the environment of accreting BHs.