Accurate evolutions of unequalmass neutronstar binaries: properties of the torus and short GRB engines
Abstract
We present new results from accurate and fully generalrelativistic simulations of the coalescence of unmagnetized binary neutron stars with various mass ratios. The evolution of the stars is followed through the inspiral phase, the merger, and the prompt collapse to a black hole, up until the appearance of a thick accretion disc, which is studied as it enters and remains in a regime of quasisteady accretion. Although a simple idealfluid equation of state with Γ = 2 is used, this work presents a systematic study within a fully generalrelativistic framework of the properties of the resulting blackholetorus system produced by the merger of unequalmass binaries. More specifically, we show that (1) the mass of the torus increases considerably with the mass asymmetry, and equalmass binaries do not produce significant tori if they have a total baryonic mass M_{tot} >~ 3.7 M_{odot}; (2) tori with masses M_{tor} ~ 0.2 M_{odot} are measured for binaries with M_{tot} ~ 3.4 M_{odot} and mass ratios q ~ 0.750.85 (3) the mass of the torus can be estimated by the simple expression \widetilde{M}_tor(q,M_{tot}) = \left[c_1 (1q) + c_2\right](M_{max}M_{tot}), involving the maximum mass for the binaries and coefficients constrained from the simulations, and suggesting that the tori can have masses as large as {\widetilde{M}}_tor \sim 0.35\,M_{\odot } for M_{tot} ~ 2.8 M_{odot} and q ~ 0.750.85 (4) using a novel technique to analyze the evolution of the tori, we find no evidence for the onset of nonaxisymmetric instabilities and that very little, if any, of their mass is unbound; (5) finally, for all the binaries considered, we compute the complete gravitational waveforms and the recoils imparted to the black holes, discussing the prospects of the detection of these sources for a number of present and future detectors.
 Publication:

Classical and Quantum Gravity
 Pub Date:
 June 2010
 DOI:
 10.1088/02649381/27/11/114105
 arXiv:
 arXiv:1001.3074
 Bibcode:
 2010CQGra..27k4105R
 Keywords:

 General Relativity and Quantum Cosmology;
 Astrophysics  High Energy Astrophysical Phenomena
 EPrint:
 35 pages