The Evolution of Supernovae in Circumstellar Wind Bubbles. II. Case of a Wolf-Rayet Star

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 expands within this modified medium. Following up on an introductory paper (Dwarkadas), herein we study the evolution of a SN in the bubble formed by a 35 M [unk] star that evolves through the phases O star, red supergiant, and Wolf-Rayet star. We model the evolution of the circumstellar medium, and the expansion of the SN shock wave within this medium. Our multidimensional simulations clearly reveal density and pressure fluctuations within the surrounding medium, the presence of hydrodynamic instabilities, the growth of vorticity, and the onset of turbulence. The SN shock interaction with this medium, and then with the dense shell, gives rise to transmitted and reflected shocks. Their effect on the X-ray emission is examined. In this particular case the shock wave is trapped in the dense shell for several doubling times. The turbulent interior, coupled with the density and pressure fluctuations, lead to a corrugated SN shock that impacts the dense shell. The impact occurs in a piecemeal fashion, with some parts of the shock wave interacting with the shell before others. As each interaction is accompanied by an increase in the X-ray and optical emission, different parts of the shell will "light up" at different times. The situation is resemblant of the scenario in SN 1987A. The reflected shock formed upon shell impact comprises several smaller shocks with different velocities, which are not necessarily moving radially inward. The spherical symmetry of the initial shock wave is completely destroyed.