*6.2. GRBs with Possible Kilonovae*

The only confirmed kilonova is associated with GRB 170817A, which is in the *Fermi*/GBM sample (Figure 9b) and does not clearly belong to either group. However, GRB 170817A was not a standard 'short' GRB, and would probably have been unremarked on if not for the associated gravitational wave source [13,14]. Near-infrared excesses, similar

to kilonova signatures, have been found in the afterglows of a handful of nearby short GRBs. Following detection in GRB 130603B [116,117], reanalysis of GRB 060614 [118,119], GRB 080503 [120] and GRB 050709 [121] revealed similar near-IR components. Since then, GRB 150101B [122], GRB 160821B [123–126] and GRB 200522A [127] have all been suggested as kilonova candidates.

Figure 9 shows that all the kilonova candidate bursts lie within Group 1 of *Swift* and *Fermi* GRBs, except for GRB 050709, for which no light curve file is available, and GRB 060614, which is in Group 2. GRB 060614 is an anomalous GRB with a short pulse followed by a longer period of soft flaring emission. Some properties of this burst are typical of the long GRB population [128], but the lack of supernova detection for this close burst (*z* = 0.125 Price et al. [129], Fugazza et al. [130]) and possible near-infrared excess led to the suggestion that this burst originates from a merger [22], or is within its own subclass [131–135]. Our results agree with the classification by Jespersen et al. [33], who place this burst in the longer-duration, collapsar group. When the T<sup>100</sup> light-curve interval is considered, the classifications remain unchanged for the kilonova candidates, with the exception of GRB 080503, which moves to Group 2. This is an example of a GRB with a short initial spike and extended emission, which may be the result of a merger rather than a collapsar [120]. The T<sup>1</sup> interval appears to return the more appropriate classification in this case.
