Generation of Strong Magnetic Fields in Axisymmetry by the Stationary Accretion Shock Instability

We begin an exploration of the capacity of the stationary accretion shock instability (SASI) to generate magnetic fields by adding a weak, stationary, and radial (but bipolar) magnetic field to a spherically symmetric fluid configuration that models a stalled shock in the post-bounce supernova environment. Upon perturbation the SASI develops, and its lateral flows alternately advect the initially radial magnetic field towards and away from the polar regions. Lateral flows into the polar regions result in partially radial outflows along the symmetry axis, and over several SASI cycles the magnetic field parallel to the axis grows—even in the absence of rotation—to dynamical significance (& 10 G), finally saturating upon local equipartition in the polar regions. While the resulting field configuration creates low-density ‘funnels’ and enables energy transport along the field through MHD waves, it does not induce qualitatively new features in the global evolution of the shock. Subject headings: supernovae: general — stars: magnetic fields — MHD — methods: numerical