What Powered the Kilonova-Like Emission After GRB 230307A in the Framework of a Neutron Star-White Dwarf Merger?

Abstract

The second brightest gamma-ray burst, GRB 230307A (with a duration $T_{90}$ ~ 40 s), exhibited characteristics indicative of a magnetar engine during the prompt emission phase. Notably, a suspected kilonova was identified in its follow-up optical and infrared observations. Here we propose that the origin of GRB 230307A is a neutron star-white dwarf (NS-WD) merger, as this could naturally interpret the long duration and the large physical offset from the center of its host galaxy. In the framework of such a NS-WD merger event, the late-time kilonova-like emission is very likely to be powered by the spin-down of the magnetar and the radioactive decay of ${}^{56}$Ni, rather than by the decay of r-process elements as these heavy elements may not be easy to be synthesized in a NS-WD merger. It is demonstrated that the above scenario can be supported by our fit to the late-time observational data, where a mass of ~ $10^{-3}{\mathrm{M}}_{\odot }$ ${}^{56}$Ni is involved in the ejecta of a mass of ~ $0.1{\mathrm{M}}_{\odot }$. Particularly, the magnetar parameters required by the fit are consistent with those derived from the early X-ray observation.

9 pages; 4 figures; Accepted by ApJL

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Cited by in corpus (4)

• A set of distinctive properties ruling the prompt emission of GRB 230307A and other long γ-ray bursts from compact object mergers
• Repeated partial disruptions in a WD-NS or WD-BH merger modulate the prompt emission of long-duration merger-type GRBs
• Shared Properties of Merger-driven Long-duration Gamma-Ray Bursts
• Gravitational waves associated with the r-mode instability from neutron star-white dwarf mergers