Fragmentation of collapsar disks and the production of gravitational waves

We argue that gravitational instability in the outer parts of collapsar disks may lead to fragmentation near the radius where helium photodisintegrates, because of the strong cooling provided by this process. This physics sets clear physical scales for the fragmentation conditions and the properties of gravitationally bound clumps. Collapse of a fragment proceeds until the neutrons become degenerate; a neutron star of mass approximate to 0.1-1M(circle dot) may result. We find that tidal disruption of a fragment and accretion by the central black hole are too rapid to account for the durations of observed X-ray flares from long gamma-ray bursts. Prior to disruption, migration of the fragment is driven by gravitational radiation and disk viscosity, which act together to produce a unique gravitational wave signature. Advanced LIGO may be able to detect such sources within approximate to 100 Mpc.