Multidimensional Simulations of the Accretion-induced Collapse of White Dwarfs to Neutron Stars

We present 2.5-dimensional radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from two-dimensional rotational equilibrium configurations, thereby accounting consistently for the effects of rotation prior to and after core collapse. We focus our study on a 1.46 and a 1.92 M sub( )a model. Electron capture leads to the collapse to nuclear densities of these cores a few tens of milliseconds after the start of the simulations. The shock generated at bounce moves slowly, but steadily, outward. Within 50-100 ms, the stalled shock breaks out of the white dwarf along the poles. The blast is followed by a neutrino-driven wind that develops within the white dwarf, in a cone of 640 opening angle about the poles, with a mass loss rate of (5-8) x 10 super(-3) M sub( )s super(-1). The ejecta have an entropy on the order of (20-50)k sub(B) baryon super(-1) and an electron fraction that is bimodal. By the end of the simulations, at 600 ms after bounce, the explosion energy has reached (3-4) x 10 super(49) ergs and the mass has reached a few times 10 super(-3) M sub( ). We estimate the asymptotic explosion energies to be lower than 10 super(50) ergs, significantly lower than those inferred for standard core collapse. The AIC of white dwarfs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion. We document in detail the numerous effects of the fast rotation of the progenitors: the neutron stars are aspherical; the "uk" and super( ) sub(e) neutrino luminosities are reduced compared to the u sub(e) neutrino luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depends strongly upon latitude (a la von Zeipel); and aquasi-Keplerian 0.1-0.5 M sub( )accretion disk is formed.