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

Abstract

Theoretically, a supra-massive neutron star or magnetar can be produced after mergers of binary neutron star. GRB 210323A is a short-duration gamma-ray burst (GRB) with a duration of lasting $\sim 1$ s. The light curve of prompt emission of GRB 210323A shows a signal-peaked structure, and a cutoff power-law model can be invoked to fit the spectra with $E_p=1826\pm 747$. More interestingly, it has an extremely long-lasting plateau emission in the X-ray afterglow with a duration of $\sim 10^{4}$ s, and then follows a rapid decay with a decay slope $\sim 3.2$. By invoking the external shock model, it is hard to explain this temporal feature of X-ray emission. In this paper, we suggest that the observed long-lasting X-ray plateau emission can be caused by the energy injection 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. This is the first short-duration GRB, whose long-lasting X-ray emission powered by a supra-massive neutron star. On the other hand, the physical parameters of a supra-massive magnetar can be roughly estimated, and compare with other short GRBs. We also discuss the possible GW emission which powered by a supra-massive magnetar and its detectability. Moreover, we calculate the possible kilonova emission which powered by R-process and magnetar spin-down to compare with the observed data.