*2.3. Fermi/GBM*

*Fermi*/GBM light curves were generated from TTE data in 64 ms and 4 ms bins using the *Fermi*-GBM Data Tools [81]. A total of 3000 bursts from 10 August 2008 to 17 March 2021 were included, with 2678 successful background subtracted light curves created. Only triggered detectors were used, and the background intervals defined in the *Fermi*/GBM catalogue were used for background subtraction. Count rates were transformed to counts s <sup>−</sup><sup>1</sup> det−<sup>1</sup> by normalising according to the number of triggered detectors. Unlike *Swift* and BATSE, *Fermi*/GBM does not have defined light curve bands. Thus, they were chosen to capture the energy ranges of the NaI and BGO detectors, and the bands were considered in hardness ratio calculations. Four energy bands were considered: the *Fermi* trigger band (50–300 keV), the lower energy band used in hardness ratio calculations (8–50 keV), the energy range of the NaI detectors (8–1000 keV) and the higher energy range of the BGO

detectors (>1000 keV). The effect of the choice of these bands was studied by repeating the analysis of light curves within the four *Swift* bands, which was shown to produce similar results.
