A Tight Three-parameter Correlation and Related Classification on Gamma-Ray Bursts

Abstract

Gamma-ray bursts (GRBs) are widely believed to be from massive collapsars and/or compact binary mergers, which accordingly, would generate long and short GRBs, respectively. The details on this classification scheme have been in constant debate given more and more observational data available to us. In this work, we apply a series of data mining methods to studying the potential classification information contained in the prompt emission of GRBs detected by the Fermi Gamma-ray Burst Monitor. A tight global correlation is found between fluence (f ), peak flux (F ) and prompt duration (T 90 ) which takes the form of log f = 0.75 log T 90 + 0.92 log F − 7.14. Based on this correlation, we can define a new parameter L = 1.66 log T 90 + 0.84 log f − 0.46 log F + 3.24 by linear discriminant analysis that would distinguish between long and short GRBs with much less ambiguity than T 90 . We also discussed the three subclasses scheme of GRB classification derived from clusters analysis based on a Gaussian mixture model, and suggest that, besides SGRBs, LGRBs may be divided into long-bright gamma-ray bursts (LBGRBs) and long-faint gamma-ray bursts (LFGRBs), LBGRBs have statistical higher f and F than LFGRBs; further statistical analysis found that LBGRBs also have higher number of GRB pulses than LFGRBs.

Two Classes of Gamma-ray Bursts Distinguished within the First Second of Their Prompt Emission

“…Type I (massive star/collapsar origin) and Type II (compact-object merger origin) bursts are defined by multiple observational criteria beyond duration and hardness [23]. Other classification methods, based on afterglow and host galaxy properties [24], minimum variability timescales [25] and prompt emission and energetics, have been defined [26][27][28][29][30]. The instrument, sample size and classification method used can lead to different results [31], and the collapsar/merger fractions for each instrument's sample cannot simply be defined by a T 90 = 2 s threshold [32].…”