Short Gamma Ray Bursts: Marking the Birth of Black Holes from Coalescing Compact Binaries.

As soon as the catalog of gamma-ray bursts (GRBs) detected by the BATSE (Burst And Transient Source Experiment) had enough events to allow a statistical study, it was discovered that GRB light curves could be separated into two families [45]. Long GRBs are characterized by a duration of more than 2 seconds and a somewhat soft spectrum. Short GRBs, on the other hand, are characterized by a duration of less than 2 seconds and a harder spectrum. Not much more could be said in the BATSE era, due to the lack of precise localizations and impossibility of long wavelength follow-up that plagued both the long and short GRB populations. With the launch of the Italian-Dutch satellite BeppoSAX, the situation for long GRBs changed dramatically. X-ray, optical and radio afterglows were discovered [16, 88, 83] to follow the prompt phase. Spectroscopy revealed that the GRBs lie at cosmological distances and that they involve explosion energies similar to core collapse supernovae [55, 46]. Evidence of beaming and association to massive stars emerged [73, 78] leading to the now widely accepted scenario of long GRBs as collimated relativistic outflows associated to Type Ib/c supernova explosions [80, 38]. Unfortunately BeppoSAX was non-optimally designed to detect short GRBs and none of the above information was available for the short bursts that remained elusive and mysterious. The only advance came from the discovery that short GRBs also have longer wavelength emission on longer timescale [47]. This discovery was however made on a stacked light curve from past events, and did not allow for any follow-up observation. A general consensus was reached in those years that short GRBs could be associated with the merger of compact binary systems [22], based on a theoretical desire more than on any robust evidence. [ABSTRACT FROM AUTHOR]