Gravitational radiation from rotational core collapse: Effects of magnetic fields and realistic equations of state

We perform a series of two-dimensional, axisymmetric, magnetohydrodynamic simulations of the rotational collapse of a supernova core. In order to calculate the waveforms of the gravitational wave, we derive the quadrupole formula including the contributions from the electromagnetic fields. Recent stellar evolution calculations imply that the magnetic fields of the toroidal components are much stronger than those of the poloidal ones at the presupernova stage. Thus we systematically investigate the effects of the toroidal magnetic fields on the amplitudes and waveforms of the gravitational wave. Furthermore, we employ two kinds of the realistic equation of states which are often used in supernova simulations. Then, we investigate the effects of the equation of states on the gravitational wave signals. As for microphysics, we take into account the electron capture and neutrino transport by the so-called leakage scheme. With these computations, we find that the peak amplitudes of the gravitational wave are lowered by an order of 10% for models with the strongest toroidal magnetic fields. However, the peak amplitudes are mostly within the sensitivity range of laser interferometers such as TAMA and the first LIGO for a source at a distance of 10 kpc. Furthermore, we point out that the amplitudes of second peaks are still within the detection limit of the first LIGO for the source, although the characteristics of second peaks are reduced by the magnetic fields. We stress the importance of the detection, since it will give us information about the angular momentum distribution of massive evolved stars. When we compare the gravitational waves from the two realistic equations of state, significant differences are not found, except that the typical frequencies of the gravitational wave become slightly higher for the softer equation of state.