2005ApJ...626..183W

We used one-dimensional radiative-transport radiation hydrodynamical (RHD) simulations to investigate the formation of clumping in freely expanding supernova ejecta due to the radioactive heating from the ⁵⁶Ni⟶⁵⁶Co⟶⁵⁶Fe decay sequence. The heating gives rise to an inflated Ni bubble, which induces a forward shock that compresses the outer ambient gas into a shell. The radiative energy deposited by the radioactivity leaks out across the shock by radiative diffusion, and we investigate its effect on the evolution of the ejecta structure. Compared to the hydrodynamical (HD) adiabatic approximation with γ=4/3, the preshock gas becomes accelerated by the radiation outflow. The shock is thus weakened and the shell becomes broader and less dense. The thickness of the shell takes up ≲4% of the radius of the bubble, and the structure of the shell can be approximately described by a self-similar solution. We compared the properties of the shell components with those of the ejecta clumps indicated by our previous HD simulations for the interaction of clumps with the outer supernova remnant. The high density contrast across the shell, χ∼100, is compatible with that of ejecta clumps as indicated for Tycho's knots, but there is insufficient dense gas to cause a pronounced protrusion on the outline of a core-collapse supernova remnant, like the bullets in the Vela remnant.