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

Binary black hole-neutron star (BHNS) binary mergers are candidate engines for both short-hard gamma-ray bursts and detectable gravitational radiation. Using our most recent conformal thin-sandwich BHNS initial data and our fully GR hydrodynamics code, which is now AMR-capable, we are able to simulate these binaries accurately through inspiral, merger, and ringdown. We explore the effects of BH spin (aligned and anti-aligned with the orbital angular momentum) by evolving binaries with BH:NS mass ratio $q=3$ that are nearly identical, except the BH spin is varied between $a/M_{\rm BH}=-0.5$ (anti-aligned) to 0.75. The number of orbits before merger increases with $a/M_{\rm BH}$. We also study the nonspinning BH case in depth, varying $q$ between 1, 3, and 5. Gravitational waveforms are calculated and compared to binary BH waveforms. Only a small disk ($< 0.01M_{\odot}$) forms for the anti-aligned spin case ($a/M_{\rm BH}=-0.5$) and for the largest mass ratio case ($q=5$). By contrast, a massive ($M_{disk}\approx 0.2M_{\odot}$), hot disk forms in the rapidly spinning $a/M_{\rm BH}=0.75$ aligned BH case. Such a disk could drive a SGRB, possibly by, e.g., producing a copious flux of $\nu-\bar{\nu}$ pairs.