GRB 210323A: Signature of Long-lasting Lifetime of Supra-massive Magnetar as the Central Engine from the Merger of Binary Neutron Star

Theoretically, a supra-massive neutron star or magnetar may be formed after the merger of binary neutron stars. GRB 210323A is a short-duration gamma-ray burst (GRB) with a duration of lasting ∼1 s. The light curve of the prompt emission of GRB 210323A shows a signal-peaked structure and a cutoff power-law model can adequately fit the spectra with E _p = 1826 ± 747. More interestingly, it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of ∼10⁴ s, and then follows a rapid decay with a decay slope ∼3.2. This temporal feature is challenging by invoking the external shock mode. In this paper, we suggest that the observed long-lasting X-ray plateau emission is caused by the energy injection of dipole radiation from supra-massive magnetar, and the abrupt decay following the long-lasting X-ray plateau emission is explained by supra-massive magnetar collapsing into a black hole. It is the short GRB (SGRB) with the longest X-ray internal plateau emission powered by a supra-massive neutron star. If this is the case, one can estimate the physical parameters of a supra-massive magnetar, and compare with other SGRBs. We also discuss the possible gravitational-wave emission, which is powered by a supra-massive magnetar and its detectability, and the possible kilonova emission, which is powered by r-process and magnetar spin-down to compare with the observed data.