A Shell Collision Scenario for EP251222b/GRB 251222A: Connecting Prompt Emission and Double-Peaked Afterglow
Year: 2026
Type: preprint
Abstract: GRB 251222A is a long-duration gamma-ray burst at a spectroscopic redshift of $z=3.171$. It was detected by the EP as the soft X-ray transient EP251222b before and during the gamma-ray emission. We performed a multi-wavelength (EP/WXT, fermi/GBM, swift/XRT and optical/NIR) investigation of this event. Its prompt soft X-ray and gamma-ray features, together with two afterglow rebrightenings, allow us to examine a possible connection between the prompt ejecta and the afterglow. We consider a multiple-shell scenario in which a faster, narrower shell catches up with a slower, wider shell. We assume that the selected pulse groups trace different ejecta and that the late X-ray flare marks their collision. Under these assumptions, we represent the post-collision outflow by an effective merged core and an outer annular component. A joint fit to the multi-band afterglow gives a Lorentz factor of $Γ_c\approx293$ for the merged core and $Γ_{1,w}\approx228$ for the outer component. The sample-wise collision mapping gives an energy release of $E_{\rm diss}=(1.6^{+2.1}_{-0.9})\times10^{52}$ erg and a dynamical dissipation efficiency of $0.37^{+0.07}_{-0.14}\%$. EP251222b can therefore be used to test a prompt--afterglow connection through shell collisions, although it does not uniquely establish this interpretation.
Source: arXiv (Cornell University)
Authors: Shi, Run, Xiao, Di, Kumar, Brajesh, Liang, Yifang, Du, Guowang, Geng, Jinjun, Zhang, Wenlong, Fang, Yuan, Guo, Chenlei, Hu, Dingfang, Hu, Jie, Huang, Qiuju, Hua, Yanlong, Huang, Yongfeng, Li, HongGuang, Liu, Xiangkun, Liu, Xiaowei, Liu, Yuan, Mao, Jirong, Mao, Xuan, Wang, Bao, Yang, Yuanpei, Zhong, Shiyan, Zhu, Dan, Wu, Xuefeng, Yuan, Weimin
Language: English
Subfield: Astronomy and Astrophysics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7222461819