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Abstract:
We present 2.5D radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from 2D rotational equilibrium configurations of a 1.46-Msun and a 1.92-Msun model. Electron capture leads to the collapse to nuclear densities of these cores within a few tens of milliseconds. The shock generated at bounce moves slowly, but steadily, outwards. Within 50-100ms, 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 ~40deg opening angle about the poles, with a mass loss rate of 5-8 x 10-3 Msun/yr. The ejecta have an entropy on the order of 20-50 kB/baryon, and an electron fraction distribution that is bimodal. By the end of the simulations, at >600ms after bounce, the explosion energy has reached 3-4 x 1049erg and the total ejecta mass has reached a few times 0.001Msun. We estimate the asymptotic explosion energies to be lower than 1050erg, 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 ``numu'' and anti-nue neutrino luminosities are reduced compared to the nue neutrino luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depend strongly upon latitude (a la von Zeipel); and a quasi-Keplerian 0.1-0.5-Msun accretion disk is formed.
