*2.2. Fermi/GBM*

The *Fermi*/GBM catalogue was accessed using the *Fermi*/GBM Data Tools [40] and limited to the period between 10 August 2008 and 17 March 2021, which yielded a sample of 3001 bursts. The hardness ratio was calculated by comparing the counts detected in the 8–50 keV band to the 50–300 keV band. Counts within the T<sup>90</sup> interval were summed from the 64 ms light curves, generated using Time-Tagged Event (TTE) data in the *Fermi*/GBM Data Tools. Only triggered detectors were used, and the background subtraction was performed using the background intervals defined in the *Fermi*/GBM catalogue. Bursts with no documented duration or incorrect background subtraction were removed, resulting in a sample of 2669 bursts. Prior to clustering, 36 outliers were identified by the R package HDOutliers [77] and removed from the sample, leaving a final sample of 2633 bursts for clustering.
