The Long and the Short of Gamma‐Ray Bursts

We report evidence from the 3B Catalogue that long ($T_{90} > 10$ s) andshort ($T_{90} < 10$ s) gamma-ray bursts represent distinct source populations.Their spatial distributions are significantly different, with long burstshaving $\langle V/V_{max} \rangle = 0.282 \pm 0.014$ but short bursts having$\langle V/V_{max} \rangle = 0.385 \pm 0.019$, differing by $0.103 \pm 0.024$,significant at the $4.3 \sigma$ level. Long and short bursts also differqualitatively in their spectral behavior, with short bursts harder in the BATSE(50--300 KeV) band, but long bursts more likely to be detected at photonenergies > 1 MeV. This implies different spatial origin and physical processesfor long and short bursts. Long bursts may be explained by accretion-inducedcollapse. Short bursts require another mechanism, for which we suggest neutronstar collisions. These are capable of producing neutrino bursts as short as afew ms, consistent with the shortest observed time scales in GRB. We brieflyinvestigate the parameters of clusters in which neutron star collisons mayoccur, and discuss the nuclear evolution of expelled and accelerated matter.Comment: 21 pp., AAS latex, 1 figure added as ps fil