Reclassification of gamma-ray bursts

Abstract

We have applied two different automatic classifier algorithms to the BATSE Current GRB Catalog data and we obtain three different classes of gamma-ray bursts (GRBs). Our results confirm the existence of a third, intermediate class of GRBs, with mean duration ∼25-50 s, as deduced from a cluster analysis and from a neural network algorithm. Our analyses imply longer durations than those found by Mukherjee et al. and Horváth, whose intermediate class had durations ∼2-10 s. From the neural network analysis no difference in hardness between the two longest classes is found, and from both methods we find that the intermediate-duration class constitutes the most homogeneous sample of GRBs in its space distribution, while the longest-duration class constitutes the most inhomogeneous one with 〈V/Vmax〉 ∼ 0.1, being thus the deepest population of GRBs with zmax ∼ 10. The trend previously found in long bursts, of spatial inhomogeneity increasing with hardness, only holds for this new longest-duration class.