*5.3. Comparison to GRB Subclasses*

Groups 1 and 2 of the *Swift*/BAT and *Fermi*/GBM samples resemble the traditional short/hard and long/soft prototypes. The groups can be compared to several subclasses of GRBs, including those with associated supernovae, extended emission episodes, and plateaus. The longer duration Group 2 contained all 49 bursts with an X-ray plateau from the platinum sample identified by Dainotti et al. [88]. Similarly, all bursts in the sample with an optical plateau [89] and those with an associated supernova and a plateau [90] lay in Group 2. The *Swift* sample analysed also contained four ultra-long GRBs from the Gold sample and five possible ultra-long GRBs from the Silver sample of Gendre et al. [91]. All of these bursts resided in Group 2 as expected, given their duration.

Short GRBs with extended emission episodes have challenged the typical durationbased classification scheme of GRBs. The population of *Swift* GRBs with extended emission identified by Gibson et al. [92] contains bursts chosen from the sample in Kaneko et al. [93] and Gompertz et al. [94,95]. The Gibson et al. [92] sample was found to only contain bursts from Group 2 of our *Swift*/BAT results. This is understandable, given that the rebrightening exhibited in their light curves can lead to an increase in the measured T<sup>90</sup> [70], thus placing them in Group 2. The extended emission episodes are typically softer than the initial spike, dominating the overall detected fluence, thus resulting in a longer duration GRB.

Group 2 resembled the standard long-duration group for both the *Swift* and *Fermi* samples. Thus, bursts with associated supernovae were expected to belong to this group. The sample of supernova-associated GRBs from Cano et al. [5] was updated to include more recent events GRB 161219B/SN 2016jca [96], GRB 171205A/SN 2017htp [97], GRB 180728A/ SN 2018fip [98,99], GRB 190114C/SN 2019jrj and GRB 190829A/AT2019oyw [100], and GRB 200826A [18–20]. There were 25 *Swift* and 15 *Fermi* GRB-SN cases within the sample analysed, all of which resided in Group 2 as expected. The only confirmed GRB with a kilonova, GRB 170817, was also in Group 1 of the *Fermi* sample.
