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When Microquasar Jets and Supernova Collide: Hydrodynamically Simulating the SS433-W50 Interaction

We present investigations of the interaction between the relativistic, precessing jets of the microquasar SS433 with the surrounding, expanding Supernova Remnant (SNR) shell W50, and the consequent evolution in the inhomogeneous Interstellar Medium (ISM). We model their evolution using the hydrodynamic FLASH code, which uses adaptive mesh refinement. We show that the peculiar morphology of the entire nebula can be reproduced to a good approximation, due to the combined effects of: (i) the evolution of the SNR shell from the free-expansion phase through the Sedov blast wave in an exponential density profile from the Milky Way disc, and (ii) the subsequent interaction of the relativistic, precessing jets of SS 433. Our simulations reveal: (1) Independent measurement of the Galaxy scale-height and density local to SS433 (as n_0 = 0.2 cm^{-3}, Z_d = 40 pc), with this scale-height being in excellent agreement with the work of Dehnen & Binney. (2) A new mechanism for hydrodynamic refocusing of conical jets. (3) The current jet precession characteristics do not simply extrapolate back to produce the lobes of W50 but a history of episodic jet activity having at least 3 different outbursts with different precession characteristics would be sufficient to produce the W50 nebula. A history of intermittent episodes of jet activity from SS433 is also suggested in a kinematic study of W50 detailed in a companion paper (Goodall et al, MNRAS submitted). (4) An estimate of the age of W50, and equivalently the age of SS433's black hole created during the supernova explosion, in the range of 17,000 - 21,000 years.