EVIDENCE THAT GAMMA-RAY BURST SOURCES REPEAT

We investigate clustering in the angular distribution of the 260 gamma-ray bursts in the publicly available BATSE catalogue, using a nearest neighbour analysis and the measures of burst brightness B and short-time-scale variability V that we introduced earlier. We find that, while all 260 bursts are only modestly clustered (Q-value= 1.8 x 10(-2)), the 202 bursts in this sample for which the statistical error in location is <9 degrees are significantly clustered on an angular scale approximate to 5 degrees (Q-value= 2.5 x 10(-4), taking into account having chosen the cut-off in the statistical error). We also find a significant correlation between bright type I bursts and faint type I and II bursts on an angular scale approximate to 5 degrees (Q-value = 4.0 x 10(-3)). This angular scale is smaller than the typical (statistical plus systematic) error in burst location of 6.degrees 8, suggesting multiple recurrences from individual sources. We conclude that 'classical' gamma-ray burst sources repeat on a time-scale of months, and that many faint type I and II bursts come from the sources of bright type I bursts.