The Large-Scale, Decelerating X-Ray Jets from the Microquasar XTE J1550—564: Evidence for External Shocks Caused by the Jet-Ism Interaction?

Abstract

Large-scale, decelerating, relativistic X-ray jets from microquasar XTE J1550—564 has been recently discovered with Chandra by Corbel et al. (2002). We find that the dynamical evolution of the approaching jet at the late time is consistent with the well-known Sedov evolutionary phase R ∝ t^2/5. A trans-relativistic external shock dynamic model by analogy with the evolution of gammaray burst remnants, is shown to be able to fit the proper-motion data of the approaching jet reasonably well. The inferred interstellar medium density around the source is well below the canonical value n_ISM ∼ 1 cm⁻³. The rapidly fading X-ray emission can be interpreted as synchrotron radiation from the non-thermal electrons in the adiabatically expanding ejecta. These electrons were accelerated by the reverse shock (moving back into the ejecta) which becomes important when the inertia of the swept external matter leads to an appreciable slowing down of the original ejecta.