*5.2. Inter-Comparison of Swift/BAT and Fermi/GBM Results*

In all three GRB samples, clear evidence of a separation into two groups by the end of the first second was observed. The clean separation of bursts in the *Swift*/BAT sample indicates that the T<sup>1</sup> interval could potentially be used to classify GRBs independently of their T<sup>90</sup> duration. The less clear-cut cluster separation found in the BATSE and *Fermi*/GBM samples most likely arose from instrumental differences (e.g., energy ranges, triggering methods and sensitivities). Of the three instruments, *Swift*/BAT has the largest effective area, and detects more spectrally softer, long-duration GRBs [101], and fewer short GRBs, than BATSE or *Fermi*/GBM [80,102].

A total of 293 bursts were analysed, which were detected by both *Fermi*/GBM and *Swift*/BAT. There is excellent (274/293) agreement between the two instruments in the cluster membership of these GRBs using the T<sup>1</sup> interval at 4 ms resolution. Differences in classification can primarily be attributed to the lack of clear separation between groups in the *Fermi*/GBM sample, which makes cluster identification less definitive than it is for *Swift*/BAT. In 6 of the 19 cases where cluster membership is found to disagree between the two detectors, significantly different (>50%) T<sup>90</sup> durations are recorded by the instruments.
