Hint of a galactic origin for a sub-population of extremely short and hard cosmic gamma-ray bursts

Abstract

Gamma Ray Bursts (GRBs) belong to an exotic class of astronomical phenomena whose origin and nature continues to puzzle the astrophysical community. These enigmatic events are seen as intense outbursts of high-energy photon radiation (10's of KeV to 10's of Mev), lasting from a few milliseconds to as long as several minutes. The understanding of gamma-ray bursts has to rely heavily on the statistical study of their properties. We have taken the BATSE 3B burst catalog for our analysis and have found a clear signature of a bimodality when bursts are classified on the basis of their time-duration and hardness-ratio. Two populations of events are suggested, one characterized by shorter bursts with harder spectra and the other by longer bursts with softer spectra. A subclass within the first group, comprising the hardest and the shortest bursts, indicate an association with some galactic feature/population.