Gamma-ray bursts, supernova kicks, and gravitational radiation

We suggest that the collapsing core of a massive rotating star may fragment to produce two or more compact objects. Their coalescence under gravitational radiation gives the resulting black hole or neutron star a significant kick velocity, which may explain those observed in pulsars. A gamma-ray burst can result only when this kick is small. Thus, only a small fraction of core-collapse supernovae produce gamma-ray bursts. The burst may be delayed significantly (hours to days) after the supernova, as suggested by recent observations. If our picture is correct, core-collapse supernovae should be significant sources of gravitational radiation with a chirp signal similar to a coalescing neutron star binary.