Post-Newtonian smoothed particle hydrodynamics calculations of binary neutron star coalescence. II. Binary mass ratio, equation of state, and spin dependence - art. no. 044012

Using our new post-Newtonian SPH (smoothed particle hydrodynamics) code, we study the final coalescence and merging of neutron star (NS) binaries. We vary the stiffness of the equation of state (EOS) as well as the initial bi nary mass ratio and stellar spins. Results are compared to those of Newtoni an calculations, with and without the inclusion of the gravitational radiat ion reaction. We find a much steeper decrease in the gravity wave peak stra in and luminosity with decreasing mass ratio than would be predicted by sim ple point-mass formulas. For a NS with a softer EOS (which we model as simp le Gamma = 2 polytropes) we find a stronger gravity wave emission, with a d ifferent morphology than for a stiffer EOS (modeled as Gamma = 3 polytropes as in our previous work). We also calculate the coalescence of NS binaries with an irrotational initial condition, and find that the gravity wave sig nal is relatively suppressed compared to the synchronized case, but shows i i very significant second peak of emission, Mass shedding is also greatly r educed, and occurs via a different mechanism than in the synchronized case. We discuss the implications of our results for gravity wave astronomy with laser interferometers such as LIGO and for theoretical models of gamma-ray bursts (GRBs) based on NS mergers.