Stellar-wind-blown Bubbles as Environments for Late-time Rebrightening of Gamma-ray Burst Afterglows

Abstract We present multiwavelength afterglow fitting results for three events that exhibit late afterglow rebrightening behavior: EP240414a ( z = 0.401), GRB 240529A ( z = 2.695), and GRB 240218A ( z = 6.782), which span a broad range of redshifts, from the local to the high-redshift Universe. We prove that the peculiar afterglow light curves of the three bursts can be well fitted by structured jets propagated in the free-to-shocked-stellar-wind environment of stellar-wind-blown bubbles. This scenario offers a self-consistent explanation for the observed subclass of afterglows that exhibit rebrightening that is characterized by steep rises and rapid decays. It also provides a unified solution for such events and offers pathways for studying both the jet generation mechanism and the propagation processes of jets through the envelope of the progenitor. This study reveals that the structured jets produced by such events exhibit a narrow jet core and a steep angle-dependent energy decay index, suggesting highly magnetized jets. The derived transition radii from free stellar winds to shocked stellar winds for all three events are smaller than 0.5 pc, with statistical analysis of similar events indicating a median value of 0.1 pc, which conflicts with numerical simulation results. We anticipate that future observations by the Einstein Probe and SVOM missions will enhance the understanding of analogous events and further reveal information about progenitors and their circum-environments.