3D simulations of strongly magnetized non-rotating supernovae: explosion dynamics and remnant properties

We investigate the impact of strong initial magnetic fields in core-collapse supernovae of non-rotating progenitors by simulating the collapse and explosion of a $16.9\, \mathrm{M}_\odot$ star for a strong- and weak-field case assuming a twisted-torus field with initial central field strengths of ${\approx }10^{12}$ and ${\approx }10^{6}\, \mathrm{G}$. The strong-field model has been set up with a view to the fossil-field scenario for magnetar formation and emulates a pre-collapse field configuration that may occur in massive stars formed by a merger. This model undergoes shock revival already $100\, \mathrm{ms}$ after bounce and reaches an explosion energy of $9.3\times 10^{50}\, \mathrm{erg}$ at $310\, \mathrm{ms}$, in contrast to a more delayed and less energetic explosion in the weak-field model. The strong magnetic fields help trigger a neutrino-driven explosion early on, which results in a rapid rise and saturation of the explosion energy. Dynamically, the strong initial field leads to a fast build-up of magnetic fields in the gain region to 40 per cent of kinetic equipartition and also creates sizable pre-shock ram pressure perturbations that are known to be conducive to asymmetric shock expansion. For the strong-field model, we find an extrapolated neutron star kick of ${\approx }350\, \mathrm{km}\, \mathrm{s}^{-1}$, a spin period of ${\approx }70\, \mathrm{ms}$, and no spin-kick alignment. The dipole field strength of the proto-neutron star is $2\times 10^{14}\, \mathrm{G}$ by the end of the simulation with a declining trend. Surprisingly, the surface dipole field in the weak-field model is stronger, which argues against a straightforward connection between pre-collapse fields and the birth magnetic fields of neutron stars.