When microquasar jets and supernova collide: hydrodynamically simulating the SS 433-W 50 interaction

We present investigations of the interaction between the relativistic, precessing jets of the microquasar SS 433 and the surrounding, expanding supernova remnant (SNR) shell, W 50, 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 scaleheight and density local to SS 433 (as n(0) = 0.2 cm(-3), Z(d) = 40 pc), with this scaleheight 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 W 50, but a history of episodic jet activity having at least three different outbursts with different precession characteristics would be sufficient to produce the W 50 nebula. A history of intermittent episodes of jet activity from SS 433 is also suggested in a kinematic study of W 50 detailed in a companion paper. (4) An estimate of the age of W 50, and equivalently the age of SS 433's black hole created during the supernova explosion, in the range of 17 000-21 000 yr.