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Studies of \textit{BATSE} bursts \citep{kouveliotou:93} have resulted in thewidespread adoption of a two-group categorization: long bursts (those withdurations $\geq 2$ seconds) and short bursts (those with durations $\leq 2$seconds). This categorization, one must recall, used the observed $T_{90}$ timedurations for bursts (during which 90\% of a burst's fluence is measured). Inthis work, we have explored two ideas: 1) a statistical search for a possiblethird, intermediate category of bursts (between the "short" and the "long"ones) among 2041 \textit{BATSE} GRBs and 757 \textit{Swift/BAT} ones, 2) astudy of bursts' intrinsic durations, where durations in the bursts' referenceframes (instead of the observed durations) are considered, for this, 248\textit{Swift/BAT} bursts that have redshift measurements were statisticallyanalyzed for the same categorization goal.  We first use a Monte Carlo method to determine the proper binning of eachGRB, considering that bursts come with different uncertainties on theirdurations. Then, using the method of minimization of chi-square $\chi^2$, wesearch for the best fit of the normalized frequency distributions$\frac{1}{N_0}\frac{dN}{d\ln{T}}$ of durations, this allows us to compare fitswith two groups ("short" and "long") with fits with three groups ("short","long", and "intermediate"). Our results indicate that the distributions ofobserved durations are better fitted by three groups than two groups for\textit{Swift/BAT} data, interestingly, the "intermediate" group appears ratherclearly for both observed and intrinsic durations. For BATSE data, thestatistical test does not prefer three groups over two. We discuss the results,their possible underlying causes, and reasonable interpretations.

Statistical Study of Observed and Intrinsic Durations among BATSE and Swift/BAT GRBs