GRB 211211A: A Neutron Star–White Dwarf Merger?

Abstract

The gamma-ray burst GRB 211211A and its associated kilonova-like emission were reported recently. A significant difference between this association event and GRB 170817A/AT 2017gfo is that GRB 211211A has a very long duration. In this Letter, we show that this association event may arise from a neutron star–white dwarf (NS–WD) merger if the central engine leaves a magnetar behind. Within the NS–WD merger, the main burst of GRB 211211A could be produced by magnetic bubble eruptions from toroidal magnetic field amplification of the premerger NS. This toroidal field amplification can be induced by the runaway accretion from the WD debris disk if the disk is in low initial entropy and efficient wind, while the extended emission of GRB 211211A is likely involved with magnetic propelling. The observed energetics and duration of the prompt emission of GRB 211211A can be fulfilled in comparison with those of accretion in a hydrodynamical thermonuclear simulation, as long as the WD has a mass ≳1M ⊙. Moreover, if the X-ray plateau in GRB afterglows is due to the magnetar spin-down radiation, GRB optical afterglows and kilonova-like emission can be jointly well modeled combining the standard forward shock with the radioactive decay power of 56Ni adding a rotational power input from the postmerger magnetar.