The black hole 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 (ISM). 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 black holes.

We present the results of a radio and X‐ray study of the Galactic microquasar GRS 1758−258, using unpublished archival data and new observations. We focus in particular on the 2000–2002 state transitions, and on its more quiet behaviour in 2008–2009. Our spectral and timing analysis of the XMM–Newton data shows that the source was in the canonical intermediate, soft and hard states in 2000 September 19, 2001 March 22 and 2002 September 28, respectively. We estimate the disc size, luminosity and temperature, which are consistent with a black hole mass ∼10 M⊙. There is much overlap between the range of total X‐ray luminosities (on average ∼0.02LEdd) in the hard and soft states, and probably between the corresponding mass accretion rates; in fact, the hard state is often more luminous. The extended radio lobes seen in 1992 and 1997 are still present in 2008–2009. The 5‐GHz radio core flux density has shown variability between ∼0.1 and 0.5 mJy over the last two decades. This firmly places GRS 1758−258 in the radio‐quiet sequence of Galactic black holes, in the radio/X‐ray plane. We note that this dichotomy is similar to the dichotomy between the radio/X‐ray sequences of Seyfert and radio galaxies. We propose that the different radio efficiency of the two sequences is due to relativistic electron/positron jets in radio‐loud black holes, and subrelativistic, thermally dominated outflows in radio‐quiet sources.

Two relativistic X-ray jets have been detected with the Chandra X-ray observatory in the black hole X-ray transient XTE J1550-564. We report a full analysis of the evolution of the two jets with a gamma-ray burst external shock model. A plausible scenario suggests a cavity outside the central source and the jets first travelled with constant velocity and then are slowed down by the interactions between the jets and the interstellar medium (ISM). The best fitted radius of the cavity is ∼0.36 pc on the eastern side and ∼0.46 pc on the western side, and the densities also show asymmetry, of ∼0.015 cm −3 on the east to ∼0.21 cm −3 on the west. Large scale low density region is also found in another microquasar system, H 1743-322. These results are consistent with previous suggestions that the environment of microquasars should be rather vacuous, compared to the normal Galactic environment. A generic scenario for microquasar jets is proposed, classifying the observed jets into three main categories, with different jet morphologies (and sizes) corresponding to different scales of vacuous environments surrounding them.