Abstract

For some short gamma-ray bursts, a non-thermal precursor flare can be observed a few seconds before mergers. The luminosity and energy of these precursors can be explained by a surface magnetic dipole of 1e13 G and the release of magnetoelastic energy when the crust breaks. A recently-proposed scenario to explain this magnetic field is that during the last seconds of a binary neutron-star merger, the tidal force can excite gravity (and inertial) modes to large amplitudes. However, existing estimates for their impact employ linear schemes which may be inaccurate for large amplitudes, as achieved by tidal resonances. In this talk, I will present the first non-linear simulations of excited gravito-inertial modes by the tidal force in a simplified rotating model. These simulations show that the axisymmetric differential rotation induced by nonlinear 2g and 1g modes may theoretically be large enough to amplify a magnetic field to ~ 1e14 G. We also find that, even without initial rotation, the neutron star would be spin-up, extending the resonance window, which might lead to higher mode amplitudes than linear predictions. Overall, these results support that resonant g-modes are able to amplify the magnetic field of a premerger neutron star, and it further suggests that g-mode resonances might have a stronger impact on gravitational-wave signals than previously estimated.