Classification of gamma-ray bursts observed with Konus-Wind

We present the analysis of duration and spectral-hardness distributions of ∼ 3000 gamma-ray bursts (GRBs) detected by Konus-Wind (KW) between November 1994 and early February 2019. We analyse burst T ₅₀ and T ₉₀ durations (the time intervals which contain the central 50% to 90% of the total burst count fluence, respectively) and argue that T ₅₀ is more robust duration measure than T ₉₀. Using a two log-normal component fit to the T ₅₀ distribution we pick the boundary between the overlapping classes of short-duration and long-duration bursts to be at T ₅₀ = 0.7 s, which implies the fraction of short GRBs (T ₅₀ < 0.7 s) to be ∼ 17%. Using Gaussian mixture model fits we show that hardness-duration distribution can be well described by three Gaussian components, with two components corresponding to short/hard and long/soft GRB population, and the third component covering the softest GRBs with intermediate durations. This classification suggests that ∼ 14% KW GRBs are from short/hard population.

Finally we discuss a possibility to discriminate between physically distinct Type I and Type II GRBs with the help of hardness-duration distribution. (paper)