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If a compact source injects relativistic plasma into its environment, it is expected that some fraction of the injected power will be dissipated by shocks, where reacceleration of particles may take place. Evidences of such interactions are the radio lobes of 1E 1740.7-2942 (Mirabel et al. 1992), GRS 1758-258 (Rodríguez et al. 1992), and the two lateral extensions in the nebula W50 that hosts at its center SS 433. The interaction of SS 433 with the shells of W50 has been studied in the X-rays (Brinkmann et al. 1996) and radio wavelengths (Dubner et al. 1998 and references therein).

Besides the well known relativistic jets seen at sub-arcsec scales in the radio, large-scale jets become visible in the X-rays at distances ~ 30 arcmin (~ 25 pc) from the compact source (Brinkmann et al. 1996). In the radio and X-rays, the lobes reach distances of up to 1° (~ 50 pc). These large-scale X-ray jets and radio lobes are the result of the interaction of the mass outflow with the interstellar medium. From optical and X-ray emission lines it is found that the sub-arcsec relativistic jets have a kinetic energy of ~ 1039 erg s-1 (Margon, 1984), which is several orders of magnitude larger than the energy radiated in the X-rays and in the radio. Dubner et al. (1998) estimate that the kinetic energy transferred into the ambient medium is ~ 2 × 1051 ergs, thus confirming that the relativistic jets from SS433 represent an important contribution to the overall energy budget of the surrounding nebula W50.

Large-scale, decelerating relativistic jets from the microquasar XTE J1550-564 have been discovered with CHANDRA by Corbel et al. (2002). The broadband spectrum of the jets is consistent with synchrotron emission from electrons with Lorentz factors of ~ 107 that are probably accelerated in the shock waves formed by the interaction of the jets with the interstellar medium. Corbel et al (2002) demonstrated that in microquasars we can study in real time the formation and dynamical evolution of the working surfaces (lobes) of relativistic jets far away from the centres of ejection, on time scales inaccessible for AGN. Working surfaces of microquasar jets as in SS433 and XTE J1550-564 are potential sources of cosmic rays.

In fact, Heinz & Sunyaev (2002) propose that if microquasar jets contain cold protons and heavy ions (as in the case of SS433) thay can produce a small but measurable contribution to the cosmic ray spectrum in the range of 3-10 GeV. These authors propose that if the cosmic ray microquasar proton component is ruled out by observations, one could put interesting constraints on the particle content in microquasar jets by the observation of the 511 keV line with INTEGRAL. The process of cosmic ray production in microquasar jets is fundamentally different from the cosmic ray production in the non relativistic shocks of supernovae remnants.

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