Axisymmetric General Relativistic Simulations of the Accretion-Induced Collapse of White Dwarfs

Ernazar Abdikamalov, Christian D. Ott, Luciano Rezzolla, Luc Dessart, Harald Dimmelmeier, A. Marek, and H.-T. Janka
Phys. Rev. D. 81, 044012 (2010), arXiv:0910.2703

- Electron Fraction Trajectories -

The accretion-induced collapse (AIC) of a white dwarf (WD) may lead to the formation of a protoneutron star and a collapse-driven supernova explosion. This process represents a path alternative to thermonuclear disruption of accreting white dwarfs in Type Ia supernovae. In the AIC scenario, the supernova explosion energy is expected to be small and the resulting transient short-lived, making it hard to detect by electromagnetic means alone. Neutrino and gravitational-wave (GW) observations may provide crucial information necessary to reveal a potential AIC. Motivated by the need for systematic predictions of the GW signature of AIC, we present results from an extensive set of general-relativistic AIC simulations using a microphysical finite-temperature equation of state and an approximate treatment of deleptonization during collapse. Investigating a set of 114 progenitor models in axisymmetric rotational equilibrium, with a wide range of rotational configurations, temperatures and central densities, and resulting white dwarf masses, we extend previous Newtonian studies and find that the GW signal has a generic shape akin to what is known as a ``Type III'' signal in the literature. Despite this reduction to a single type of waveform, we show that the emitted GWs carry information that can be used to constrain the progenitor and the postbounce rotation. We discuss the detectability of the emitted GWs, showing that the signal-to-noise ratio for current or next-generation interferometer detectors could be high enough to detect such events in our Galaxy. Furthermore, we contrast the GW signals of AIC and rotating massive star iron core collapse and find that they can be distinguished, but only if the distance to the source is known and a detailed reconstruction of the GW time series from detector data is possible. Some of our AIC models form massive quasi-Keplerian accretion disks after bounce. The disk mass is very sensitive to progenitor mass and angular momentum distribution. In rapidly differentially rotating models whose precollapse masses are significantly larger than the Chandrasekhar mass, the resulting disk mass can be as large as ~0.8 solar masses. Slowly and/or uniformly rotating models that are limited to masses near the Chandrasekhar mass produce much smaller disks or no disk at all. Finally, we find that the postbounce cores of rapidly spinning white dwarfs can reach sufficiently rapid rotation to develop a gravito-rotational bar-mode instability. Moreover, many of our models exhibit sufficiently rapid and differential rotation to become subject to recently discovered low-E_rot/|W|-type dynamical instabilities.


Here we provide the electron fraction (Y_e) profiles used in the deleptonization scheme described in detail in the paper. The Y_e data were obtained in the Newtonian multi-group flux-limited diffusion neutrino radiation-hydrodynamics AIC simulations of Dessart et al. 2006.

1.46 M_Sun model, T_0 = T_c = 1.3d10 K download Y_e(rho)
1.46 M_Sun model, T_0 = T_c = 1.0d10 K download Y_e(rho)
1.46 M_Sun model, T_0 = T_c = 5.0d9 K download Y_e(rho)
1.92 M_Sun model, T_0 = T_c = 1.3d10 K download Y_e(rho)
1.92 M_Sun model, T_0 = T_c = 5.0d9 K download Y_e(rho)

Below are the Y_e(rho) data used to setup the initial white dwarf Y_e distribution. They are based on data of Dessart et al. 2006 at 7 ms into their simulation.

T_0 = T_c = 1.0d10 K download Y_e(rho)
T_0 = T_c = 5.0d9 K download Y_e(rho)