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General Relativity and Quantum Cosmology, gr-qc, Astrophysics, High Energy Astrophysical Phenomena, astro-ph.HE
Abstract:
We present a model for determining the dimensionless spin parameter and mass
of the black hole remnant of black hole-neutron star mergers with parallel
orbital angular momentum and initial black hole spin. This approach is based on
the Buonanno, Kidder, and Lehner method for binary black holes and it is
successfully tested against the results of numerical-relativity simulations:
the dimensionless spin parameter is predicted with absolute error $\lesssim
0.02$, whereas the relative error on the final mass is $\lesssim 2$%, its
distribution being pronouncedly peaked at 1%. Our approach and the fit to the
torus remnant mass reported in Foucart (2012) thus constitute an easy-to-use
analytical model that accurately describes the remnant of BH-NS mergers. We
investigate the space of parameters consisting of the binary mass ratio, the
initial black hole spin, and the neutron star mass and equation of state. We
provide indirect support to the cosmic censorship conjecture for black hole
remnants of black hole-neutron star mergers. We show that the presence of a
neutron star affects the quasi-normal mode frequency of the black hole remnant,
thus suggesting that the ringdown epoch of the gravitational wave signal may
virtually be used to (1) distinguish binary black hole from black hole-neutron
star mergers and to (2) constrain the neutron star equation of state.
