The Advective-Acoustic instability in type II Supernovae

The puzzle of birth velocities of pulsars (pulsar kicks) could be solved by an asymmetric explosion of type II Supernovae. We propose a simple hydrodynamical mechanism in order to explain this asymmetry, through the advective-acoustic cycle (Foglizzo 2002) : during the phase of stalled shock, an instability based on the cycle between advected perturbations (entropy / vorticity) and acoustic perturbations can develop between the shock and the surface of the nascent neutron star. Eigenfrequencies are computed numerically, improving the calculation of Houck & Chevalier (1992). The linear instability is dominated by a mode l=1, as observed in the numerical simulations of Blondin et al. (2003) and Scheck et al. (2004). The frequency dependence of the growth rate reveals the presence of the advective-acoustic cycle.