Radio Lobe Dynamics and the Environment of Microquasars
  We argue that, when compared to AGNs in dynamical terms, microquasars are found in low density, low pressure environments. Using a simple analytic model, we discuss radio lobe dynamics and emission. Dynamical considerations for GRS 1915+105 and GRO J1655-40 show that they are located in ISM densities well below the canonical n_ISM ~ 1 cm^{-3} unless the jets are unusually narrow or much more powerful than currently believed. 
S. Heinz