Instabilities in neutron stars with toroidal magnetic fields

We study m= 1 oscillations and instabilities of magnetized neutron stars, by numerical time evolution of linear perturbations of the system. The background stars are stationary equilibrium configurations with purely toroidal magnetic fields. We find that an m= 1 instability of toroidal magnetic fields, already known from local analyses, may also be found in our relatively low-resolution global study. We present quantitative results for the instability growth rate and its suppression by rotation. The instability is discussed as a possible trigger mechanism for soft gamma repeater flares. Although our primary focus is evolutions of magnetized stars, we also consider perturbations about unmagnetized background stars in order to study m= 1 inertial modes. We track these modes up to break-up frequency Ω_K, extending known slow-rotation results.