Sphericization of the remnants of an asymmetric supernova outburst in a homogeneous medium

Numerical calculations have been performed in the 1.5-dimensional hydrodynamics approximation to analyze the sphericization of a shock wave, initially asymmetric in both form and velocity, which is propagated through a homogeneous interstellar medium. Three different approaches to the problem are considered, with preference given to the snowplow model. The time scale for the shock to sphericize is determined for various ISM densities and explosion parameters. If the initial asymmetry is strong enough, then even when the shock has become spherical in shape a substantial difference will persist in the surface density at the pole and at the equator, possibly explaining features observed in the supernova remnant Cassiopeia A.