SIMBAD references

Traditionally, gamma-ray bursts (GRBs) are classified as long and short GRBs, with T₉₀ = 2 s being the threshold duration. Generally, long-duration GRBs (LGRBs; T₉₀ > 2 s) are associated with the collapse of massive stars, and short-duration (SGRBs; T₉₀ < 2 s) are associated with compact binary mergers involving at least one neutron star. However, the existence of a population of so-called “peculiar GRBs”-i.e., LGRBs originating from mergers or long Type I GRBs, and SGRBs originating from collapsars or short Type II GRBs-has challenged the traditional paradigm of GRB classification. Finding more peculiar GRBs may help to give more insight into this issue. In this work, we analyze the properties of machine-learning-identified long Type I GRB and short Type II GRB candidates, long GRBs-I and short GRBs-II (the so-called “peculiar GRBs”). We find that long GRBs-I almost always exhibit properties similar to Type I GRBs, which suggests that mergers may indeed produce GRBs with T₉₀ > 2 s. Furthermore, according to the probability given by the redshift distribution, short GRBs-II almost exhibit properties similar to Type II GRBs. This suggests that the populations of short Type II GRBs are not scarce and that they are hidden in a large number of samples without redshifts, which is unfavorable for the interpretation that the jet progression leads to a missed main emission.