*Relativistic Simulations of Black Hole-Neutron Star Mergers: Effects
of Black-Hole Spin*

** Zachariah B.
Etienne
Yuk Tung Liu
Stuart L.
Shapiro
Thomas W.
Baumgarte**

**ABSTRACT**

Black hole-neutron star (BHNS) binary mergers are candidate engines for
generating both short-hard gamma-ray bursts (SGRBs) and detectable
gravitational waves. Using our most recent conformal thin-sandwich BHNS
initial data and our fully general relativistic hydrodynamics code,
which is now AMR-capable, we are able to efficiently and accurately
simulate these binaries from large separations through inspiral, merger,
and ringdown. We evolve the metric using the BSSN formulation with the
standard moving puncture gauge conditions and handle the hydrodynamics
with a high-resolution shock-capturing scheme. We explore the effects of
BH spin (aligned and anti-aligned with the orbital angular momentum) by
evolving three sets of initial data with BH:NS mass ratio q=3: the data
sets are nearly identical, except the BH spin is varied between a/M = -0.5 (anti-aligned), 0.0, and 0.75. The
number of orbits before merger increases with a/M, as expected. We also
study the nonspinning BH case in more detail, varying q between 1, 3,
and 5. We calculate gravitational waveforms for the cases we simulate
and compare them to binary black-hole waveforms. Only a small disk (<
0.01 M_{sun}) forms for the anti-aligned spin case (a/M = -0.5) and for the most extreme mass ratio
case (q=5). By contrast, a massive (M_{disk} is about 0.2 M_{sun}), hot disk
forms in the rapidly spinning (a/M = 0.75)
aligned BH case. Such a disk could drive a SGRB, possibly by, e.g.,
producing a copious flux of neutrino-antineutino pairs.

Phys.Rev.D79:044024 (2009), arXiv:0812.2245v2

Case A a/M = 0.00, mass ratio q = 3.00

Case B a/M = 0.75, mass ratio q = 3.00

Case C a/M = -0.50, mass ratio q = 3.00

Case D a/M = 0.00, mass ratio q = 5.00

Case E a/M = 0.00, mass ratio q = 1.00

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