Why do some compact-binary mergers produce long gamma-ray bursts?
In plain words
Long bursts are usually linked to collapsing massive stars, but GRB 060614 in 2006 showed no supernova, and two long bursts in 2021 and 2023 were followed by kilonovae, the glow of radioactive debris from neutron-star mergers.
Precise statement
GRB 060614, GRB 211211A and GRB 230307A had prompt durations of tens of seconds or more and no supernova to deep limits; the latter two showed kilonova emission. Determine what extends engine activity far beyond the $\sim 0.1 \text{ to } 1\,\mathrm{s}$ viscous time of a merger disk: a long-lived magnetar remnant, a neutron star-white dwarf or neutron star-black hole merger with a massive disk, or magnetic flux evolution in the disk. Answer: a mechanism with predicted duration distribution and rate.
What would settle it
Gravitational-wave detection of a merger coincident with a long GRB, fixing the binary type and remnant.
Status in the literature
2023: JWST spectra of the GRB 230307A kilonova showed a feature attributed to tellurium, supporting merger r-process ejecta.