First model to connect the underlying binary merger population with the observed compact binary GRB (cbGRB) sub-classes and explain the origin of the recent puzzling detection of lGRBs accompanied by kilonovae. Shown are the merger products as a function of binary mass ratio q (vertical axis) and total mass Mtot (horizontal axis). lGRBs occur in high- Mtot and high-q BNS mergers that form massive BH disks of Md ∼ 10−1 M⊙, or in high pre-merger BH spin and low-q BH–NS mergers (blue region). sGRBs may arise either from q ∼ 1 BNS mergers (bottom yellow region), low pre-merger BH spin/high-q BH–NS mergers (top yellow region), or HMNSs formed in BNS mergers with Mtot ≲ 2.8 M⊙ (left yellow region). If BH-powered jets are unlike HMNS-powered jets, then the absence of evidence for distinct sub-classes of sGRBs suggests that either BHs or HMNSs are likely to be the sole origin of these events, i.e., only one of the possible sGRB scenarios is correct. The Galactic BNS mass distribution, the bimodal GRB duration distribution, and GW170817 observations imply that HMNSs are likely the most common remnant of BNS mergers, and are likely the engines of sGRB jets [42].
