The Evolution of Supernovae in Circumstellar Wind Bubbles II: Case of a Wolf-Rayet star

Abstract

(Abridged) Mass-loss from massive stars leads to the formation of circumstellar wind-blown bubbles surrounding the star, bordered by a dense shell. When the star ends its life in a supernova (SN) explosion, the resulting shock wave will interact with this modified medium. In a previous paper we discussed the basic parameters of this interaction. In this paper we go a step further and study the evolution of SNe in the wind blown bubble formed by a 35 $\msun$ star that starts off as an O star, goes through a red supergiant phase, and ends its life as a Wolf-Rayet star. We model the evolution of the CSM and then the expansion of the SN shock wave within this medium. Our simulations clearly reveal fluctuations in density and pressure within the surrounding medium. The SN shock interacting with these fluctuations, and then with the dense shell surrounding the wind-blown cavity, gives rise to a variety of transmitted and reflected shocks in the wind bubble. The interactions between these various shocks and discontinuities is examined, and its effects on the X-ray emission is noted. Our simulations reveal the presence of several hydrodynamic instabilities. They show that the turbulent interior, coupled with the large fluctuations in density and pressure, gives rise to an extremely corrugated SN shock wave. The shock shows considerable wrinkles as it impacts the dense shell, and the impact occurs in a piecemeal fashion, with some parts of the shock wave interacting with the shell before the others. Therefore different parts of the shell will `light-up' at different times. The non-spherical nature of the interaction means that it will occur over a prolonged period of time, and the spherical symmetry of the initial shock wave is destroyed.