Hydrodynamic simulations of the merger of stellar mass black hole – neutron star binaries ( BH/NS ) are compared with mergers of binary neutron stars ( NS/NS ) .
The simulations are Newtonian , but take into account the emission and backreaction of gravitational waves .
The use of a physical nuclear equation of state allows us to include the effects of neutrino emission .
For low neutron star to black hole mass ratios the neutron star transfers mass to the black hole during a few cycles of orbital decay and subsequent widening before finally being disrupted , whereas for ratios near unity the neutron star is already distroyed during its first approach .
A gas mass between \sim 0.3 M _ { \odot } and \sim 0.7 M _ { \odot } is left in an accretion torus around the black hole and radiates neutrinos at a luminosity of several 10 ^ { 53 } erg/s during an estimated accretion time scale of about 0.1 s. The emitted neutrinos and antineutrinos annihilate into e ^ { \pm } pairs with efficiencies of 1–3 % percent and rates of up to \sim 2 \times 10 ^ { 52 } erg/s , thus depositing an energy E _ { \nu \bar { \nu } } \lesssim 10 ^ { 51 } erg above the poles of the black hole in a region which contains less than 10 ^ { -5 } M _ { \odot } of baryonic matter .
This could allow for relativistic expansion with Lorentz factors around 100 and is sufficient to explain apparent burst luminosities L _ { \gamma } \sim E _ { \nu \bar { \nu } } / ( f _ { \Omega } t _ { \gamma } ) up to several 10 ^ { 53 } { erg s } ^ { -1 } for burst durations t _ { \gamma } \approx 0.1 –1 s , if the \gamma emission is collimated in two moderately focussed jets in a fraction f _ { \Omega } = 2 \delta \Omega / ( 4 \pi ) \approx 1 / 100 — 1 / 10 of the sky .