Investigation on the Bimodal Distribution of the Duration of Gamma-ray Bursts from BATSE Light Curves

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We have investigated the bimodal distribution of the duration of BATSE gamma-ray bursts (GRBs) by analyzing light curves of 64 ms time resolution. We define the average pulse width of GRBs from the auto-correlation function of GRB profiles. The distribution of the average pulse width of GRBs is bimodal, suggesting that GRBs are composed of long-pulse GRBs and short-pulse GRBs. The average pulse width of long-pulse GRBs appears correlated with the peak flux, consistent with the time dilation effect anticipated from the cosmological origin of GRBs. However, the correlation between the average pulse width and the peak flux for the short-pulse GRBs doesn't show such a tendency, which needs further study with higher time resolution data.