Matter mixing in aspherical core-collapse supernovae: A search for possible conditions for conveying 56Ni into high velocity regions

We perform two-dimensional axisymmetric hydrodynamic simulations of matter mixing in aspherical core-collapse supernova explosions of a 16.3 M ☉ star with a compact hydrogen envelope. Observations of SN 1987A have provided evidence that 56Ni synthesized by explosive nucleosynthesis is mixed into fast moving matter (3500 km s–1) in the exploding star. In order to clarify the key conditions for reproducing such high velocity of 56Ni, we revisit matter mixing in aspherical core-collapse supernova explosions. Explosions are initiated artificially by injecting thermal and kinetic energies around the interface between the iron core and the silicon-rich layer. Perturbations of 5% or 30% amplitude in the radial velocities are introduced at several points in time. We find that no high velocity 56Ni can be obtained if we consider bipolar explosions with perturbations (5% amplitude) of pre-supernova origins. If large perturbations (30% amplitude) are introduced or exist due to some unknown mechanism in a later phase just before the shock wave reaches the hydrogen envelope, 56Ni with a velocity of 3000 km s–1 can be obtained. Aspherical explosions that are asymmetric across the equatorial plane with clumpy structures in the initial shock waves are investigated. We find that the clump sizes affect the penetration of 56Ni. Finally, we report that an aspherical explosion model that is asymmetric across the equatorial plane with multiple perturbations of pre-supernova origins can cause the penetration of 56Ni clumps into fast moving matter of 3000 km s–1. We show that both aspherical explosions with clumpy structures and perturbations of pre-supernova origins may be necessary to reproduce the observed high velocity of 56Ni. To confirm this, more robust three-dimensional simulations are required.