A Shell Collision Scenario for EP251222b/GRB 251222A: Connecting Prompt Emission and Double-Peaked Afterglow
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 Γc≈293 for the merged core and Γ1,w≈228 for the outer component. The sample-wise collision mapping gives an energy release of Ediss=(1.6+2.1−0.9)×1052 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.
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BibTeX
@misc{shi2026shell,
title = {{A Shell Collision Scenario for EP251222b/GRB 251222A: Connecting Prompt Emission and Double-Peaked Afterglow}},
author = {Run Shi and Di Xiao and Brajesh Kumar and Yifang Liang and Guowang Du and Jinjun Geng and Wenlong Zhang and Yuan Fang and Chenlei Guo and Dingfang Hu and Jie Hu and Qiuju Huang and Yanlong Hua and Yongfeng Huang and HongGuang Li and Xiangkun Liu and Xiaowei Liu and Yuan Liu and Jirong Mao and Xuan Mao and Bao Wang and Yuanpei Yang and Shiyan Zhong and Dan Zhu and Xuefeng Wu and Weimin Yuan},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.21583},
eprint = {2610.21583},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.21583},
}
RIS
TY - UNPB
TI - A Shell Collision Scenario for EP251222b/GRB 251222A: Connecting Prompt Emission and Double-Peaked Afterglow
AU - Run Shi
AU - Di Xiao
AU - Brajesh Kumar
AU - Yifang Liang
AU - Guowang Du
AU - Jinjun Geng
AU - Wenlong Zhang
AU - Yuan Fang
AU - Chenlei Guo
AU - Dingfang Hu
AU - Jie Hu
AU - Qiuju Huang
AU - Yanlong Hua
AU - Yongfeng Huang
AU - HongGuang Li
AU - Xiangkun Liu
AU - Xiaowei Liu
AU - Yuan Liu
AU - Jirong Mao
AU - Xuan Mao
AU - Bao Wang
AU - Yuanpei Yang
AU - Shiyan Zhong
AU - Dan Zhu
AU - Xuefeng Wu
AU - Weimin Yuan
PY - 2026
DA - 2026/10/15
PB - arXiv
DO - 10.48550/arxiv.2610.21583
UR - https://arxiv.org/abs/2610.21583
AB - 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≈293 for the merged core and Γ_1,w≈228 for the outer component. The sample-wise collision mapping gives an energy release of E_diss=(1.6^+2.1_−0.9)×10^52 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.
ER -