General Relativistic Simulations of Accretion Induced Collapse of Neutron Stars to Black Holes. (arXiv:1209.0783v1 [astro-ph.HE])

General Relativistic Simulations of Accretion Induced Collapse of Neutron Stars to Black Holes. (arXiv:1209.0783v1 [astro-ph.HE]):
Neutron stars (NSs) in the astrophysical Universe are often surrounded by
accretion disks. Accretion of matter onto a NS may increase its mass above the
maximum value allowed by its equation of state, inducing its collapse to a
black hole (BH). Here we study this process for the first time, in 3D, and in
full general relativity. By considering three initial NS configurations, each
with and without a surrounding disk (of mass ~7% M_{NS}), we investigate the
effect of the accretion disk on the dynamics of the collapse and its imprint on
both the gravitational wave (GW) and electromagnetic (EM) signals that can be
emitted by these sources. We show in particular that, even if the GW signal is
similar for the accretion induced collapse (AIC) and the collapse of a NS in
vacuum (and detectable only for Galactic sources), the EM counterpart could
allow to discriminate between these two types of events. In fact, our
simulations show that, while the collapse of a NS in vacuum leaves no
appreciable baryonic matter outside the event horizon, an AIC is followed by a
phase of rapid accretion of the surviving disk onto the newly formed BH. The
post-collapse accretion rates, on the order of ~10^{-2} M_{sun} s^{-1}, make
these events tantalizing candidates as engines of short Gamma-Ray Bursts.