Collapse of Neutron Stars to Black Holes in Binary Systems: A Model for Short Gamma Ray Bursts

The accretion of ~ 0.1 -- 1 M_o of material by a neutron star through Roche lobe overflow of its companion or through white-dwarf/neutron-star coalescence in a low mass binary system could be enough to exceed the critical mass of a neutron star and trigger its collapse to a black hole, leading to the production of a short gamma-ray burst (SGRB). In this model, SGRBs would often be found in early-type galaxies or in globular cluster environments, though they could also be formed through stellar-wind accretion in high-mass binary systems of star-forming galaxies. Although the collapse event is likely to be of short (<< 1 s) duration, afterglow complexity could be produced by neutron decoupling in the fireball and subsequent accretion of the companion remnant, for example, the disrupted white-dwarf core.