Models of rapidly rotating neutron stars: remnants of accretion-induced collapse

Equilibrium models of differentially rotating nascent neutron stars are con structed, which represent the result of the accretion-induced collapse of r apidly rotating white dwarfs. The models are built in a two-step procedure: (1) a rapidly rotating pre-collapse white dwarf model is constructed; (2) a stationary axisymmetric neutron star having the same total mass and angul ar momentum distribution as the white dwarf is constructed. The resulting c ollapsed objects consist of a high-density central core of size roughly 20 km, surrounded by a massive accretion torus extending over 1000 km from the rotation axis. The ratio of the rotational kinetic energy to the gravitati onal potential energy of these neutron stars ranges from 0.13 to 0.26, sugg esting that some of these objects may have a non-axisymmetric dynamical ins tability that could emit a significant amount of gravitational radiation.