The Spherical Accretion Shock Instability, or SASI, is a hydrodynamic instability discovered by Blondin, Mezzacappa & DeMarino (2003) in their numerical study of the stalled accretion shock in core-collapse supernovae. In 2D axisymmetry this instability drives an initially spherical accretion shock into a 'sloshing' mode in which it oscillates up and down the symmetry axis. This phenomenon has subsequently been seen in a variety of supernova simulations by numerous authors.
Non-Axisymmetric Modes were first seen in 3D simulations of a stationary spherical accretion shock (Blondin & Mezzacappa 2007). That work also demonstrated that a moderate rotation in the progenitor star led to a much quicker dominance of the spiral SASI. These non-axisymmetric modes (the spiral patterns on the left) were studied in detail by Blondin & Shaw (2007), who used 2D simulations in the equatorial plane of a spherical grid to quantify the growth rates and verify the linear nature of these 'm' modes. They also showed that, in this restricted 2D geometry, the axisymmetric mode is a linear combination of two oppositely-directed spiral waves.
The goal of this work is to quantify the linear growth of the SASI in 3D and characterize its nonlinear evolution.
