On the Formation of SS433

Abstract: SS433 is an extraordinary X-ray binary which is ejecting bipolar jets with $26\%$ of the speed of light. Associated with the supernova-like shell W50, SS433 is also probably one of the youngest X-ray binaries with an age of $\lesssim 10^5$ yr. However, the masses of the two components in SS433 and even the nature of the compact object are still under debate. In this work, assuming that the compact object is a black hole, we employ a binary population synthesis method to study the formation of SS433. We use previous estimates of the age of W50 and the duration of the jet activity to constrain the evolutionary history. Our calculations suggest that SS433 likely harboured a Hertzsprung gap star at the beginning of the current Roche-lobe overflow phase. The masses of the black hole and the optical/donor star in SS433 suggested by the simulations are around $8\ M_{\odot}$ and $24\ M_{\odot}$, respectively. Future measurement of the donor mass and radius can help infer not only the orgin of the binary but also the nature of the nebula W50.