NICKEL BUBBLE EXPANSION IN TYPE Ia SUPERNOVAE: ADIABATIC SOLUTIONS

This study investigates the expansion properties of nickel (Ni) bubbles in Type Ia supernovae (SNe Ia) due to radioactive heating from the Ni → Co → Fe decay sequence, under the spherically symmetric approximation. An exponentially-declining medium is considered as the ejecta substrate, allowing for the density gradient expected in a Type Ia supernova (SN Ia). The heating gives rise to an inflated Ni bubble, which induces a forward shock that compresses the outer ambient gas into a shell. As the heating saturates, the flow tends toward a freely-expanding state with the structure frozen into the ejecta. The thickness of the shell is ∼ 1% of the radius of the bubble, and the density contrast across the shell reaches χ & 100 in a narrow region that is limited by numerical resolution. In the adiabatic case (in which no radiative energy diffuses across the shell) the structure of the shell can be approximately described by a self-similar solution that is determined by the expansion rate and ambient density gradient of the shell. In the radiative case, the shell expansion weakens but remains comparable to the adiabatic solution. The density contrast of the inferred ejecta clumps (shell components) is greater than that given by the model that uses a uniform ejecta substrate, while the interaction of the clumps with the remnant is delayed to a more advanced evolutionary stage. The explosion parameters of the SN are varied to examine whether the created clump characteristics are consistent with those of the ejecta knots that are present at the edges of Tycho’s remnant. Explosion conditions similar to those of successful explosion models are found, including the deflagration W7 and the delayed detonation yield with sufficient ejection velocities as well as timely initiations for the clump-remnant interaction, whereas the luminous helium (He) detonations and the low-energy Chandrasekhar-mass