SIMBAD references

Using Gaussian Mixture Model (GMM) and expectation-maximization algorithm, we perform an analysis of time duration (T₉₀) for Compton Gamma Ray Observatory(CGRO)/BATSE, Swift/BAT and Fermi/GBM gamma-ray bursts (GRBs). The T₉₀ distributions of 298 redshift-known Swift/BAT GRBs have also been studied in both observer and rest frames. Bayesian information criterion has been used to compare between different GMM models. We find that two Gaussian components are better to describe the CGRO/BATSE and Fermi/GBM GRBs in the observer frame. Also, we caution that two groups are expected for the Swift/BAT bursts in the rest frame, which is consistent with some previous results. However, Swift GRBs in the observer frame seem to show a trimodal distribution, of which the superficial intermediate class may result from the selection effect of Swift/BAT.