The progenitor and central engine of a peculiar GRB 230307A

Recently, a lack of supernova-associated long-duration gamma-ray burst (GRB 230307A) at such a low redshift $z=0.065$, but associated with a possible kilonova emission, has attracted great attention. Its heavy element nucleosynthesis and the characteristic of soft X-ray emission suggests that the central engine of GRB 230307A is magnetar which is originated from a binary compact star merger. The calculated lower value of ε ~ 0.05 suggests that the GRB 230307A seems to be with ambiguous progenitor. The lower value of feff=1.23 implies that the GRB 230307A is not likely to be from the effect of "tip of iceberg". We adopt the magnetar central engine model to fit the observed soft X-ray emission with a varying efficiency and find that the parameters constraints of magnetar fall into a reasonable range, i.e., B<9.4×10¹⁵ G and $P<2.5$ ms for Γₛₐₜ = 10³, and B<3.6×10¹⁵ G and $P<1.05$ ms for Γₛₐₜ = 10⁴. Whether the progenitor of GBR 230307A is from the mergers of neutron star - white dwarf (NS - WD) or neutron star - neutron star (NS - NS) remains unknown.