Signature of Strange Star as the Central Engine of GRB 240529A

Abstract GRB 240529A is a long-duration gamma-ray burst (GRB) whose light curve of prompt emission is composed of a triple-episode structure, separated by quiescent gaps of tens to hundreds of seconds. More interestingly, its X-ray light curve of afterglow exhibits two plateau emissions, namely, an internal plateau emission that is smoothly connected with a ∼ t −0.1 segment and followed by a ∼ t −2 power-law decay. The three episodes in the prompt emission, together with two plateau emissions in X-ray, are unique in the Swift era. They are very difficult to explain with the standard internal/external shock model by invoking a black hole central engine. However, it could be consistent with the prediction of a supramassive magnetar as the central engine, the physical process of phase transition from a magnetar to a strange star, as well as the cooling and spin-down of the strange star. In this paper, we propose that the first- and second-episode emissions in the prompt gamma ray of GRB 240529A are from the jet emission of a massive star collapsing into a supramassive magnetar and the reactivity of the central engine, respectively. Then, the third-episode emission of the prompt is attributed to the phase transition from a magnetar to a strange star. Finally, the first and second plateau emissions of the X-ray afterglow are powered by the cooling and spin-down of the strange star, respectively. The observational data of each component of GRB 240529A are roughly coincident with the estimations of the above physical picture.