We systematically perform the merger simulation of black hole-neutron star ( BH-NS ) binaries in full general relativity , focusing on the case that the NS is tidally disrupted .
We prepare BH-NS binaries in a quasicircular orbit as the initial condition in which the BH is modeled by a nonspinning moving puncture .
For modeling the NS , we adopt the \Gamma -law equation of state with \Gamma = 2 and the irrotational velocity field .
We change the BH mass in the range M _ { BH } \approx 3.3 – 4.6 M _ { \odot } , while the rest mass of the NS is fixed to be M _ { * } = 1.4 M _ { \odot } ( i.e. , the NS mass M _ { NS } \approx 1.3 M _ { \odot } ) .
The radius of the corresponding spherical NS is set in the range R _ { NS } \approx 12 –15 km ( i.e. , the compactness GM _ { NS } / R _ { NS } c ^ { 2 } \approx 0.13 –0.16 ) .
We find for all the chosen initial conditions that the NS is tidally disrupted near the innermost stable circular orbit .
For the model of R _ { NS } = 12 km , more than 97 % of the rest mass is quickly swallowed into the BH and the resultant torus mass surrounding the BH is less than 0.04 M _ { \odot } .
For the model of R _ { NS } \approx 14.7 km , by contrast , the torus mass is about 0.16 M _ { \odot } for the BH mass \approx 4 M _ { \odot } .
The thermal energy of the material in the torus increases by the shock heating occurred in the collision between the spiral arms , resulting in the temperature 10 ^ { 10 } – 10 ^ { 11 } K. Our results indicate that the merger between a low-mass BH and its companion NS may form a central engine of short gamma-ray bursts ( SGRBs ) of the total energy of order 10 ^ { 49 } ergs if the compactness of the NS is fairly small \lesssim 0.145 .
However , for the canonical values M _ { NS } = 1.35 M _ { \odot } and R _ { NS } = 12 km , the merger results in small torus mass , and hence , it can be a candidate only for the low-energy SGRBs of total energy of order 10 ^ { 48 } ergs .
We also present gravitational waveforms during the inspiral , tidal disruption of the NS , and subsequent evolution of the disrupted material .
We find that the amplitude of gravitational waves quickly decreases after the onset of tidal disruption .
Although the quasinormal mode is excited , its gravitational wave amplitude is much smaller than that of the late inspiral phase .
This reflects in the fact that the spectrum amplitude sharply falls above a cut-off frequency which is determined by the tidal disruption process .
We also find that the cut-off frequency is 1.25–1.4 times larger than the frequency predicted by the study for the sequence of the quasicircular orbits and this factor of the deviation depends on the compactness of the NS .