2009MNRAS.396L..81V

The HETE II and Swift discoveries of long gamma-ray bursts (GRBs) with and without supernovae reveal a diversity in their astronomical origin with otherwise a common inner engine. The durations, spectral-energy correlations and light curves in gamma-rays are in remarkable agreement with viscous spin-down of stellar mass black holes against surrounding high-density matter, as may ensue in core collapse of massive stars and by tidal break-up of neutron stars in mergers with a companion black hole or another neutron star. While mergers produce a preceding positive chirp in gravitational-wave emissions, black hole spin-down produces a negative chirp in relaxation to a nearly Schwarzschild black hole, followed by quasi-normal mode ringing of the event horizon. Chirps hereby provide unambiguous identification of the origin of long GRBs.