arXiv · 2606.10014
X-rays breaking out of pre-explosion ejecta mark a supernova's first light
Abstract
Massive stars die as core-collapse supernovae, whose optical light emerges days after the implosion. Theory predicts that the initial collapse-driven shock, upon breaking through the star and dense circumstellar medium, emits a brief thermal flash of soft X-rays and ultraviolet. Yet these elusive first signals have remained largely undetected, owing to limited wide-field soft X-ray monitoring. Here we report the discovery of a soft X-ray flash, EP260321a, followed days later by a broad-lined supernova from an envelope-stripped progenitor. Its X-ray spectrum, best modeled with blackbody, establishes it as the long-sought archetypal shock breakout. The burst's duration and energetics place the breakout at a radius of 300 solar radii, tracing a dense surrounding shell and revealing abrupt mass ejection within the final month before collapse.
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Weimin Yuan, Qiu-Ju Huang, Jin-Ping Zhu, Yun-Wei Yu, Dong Xu, Chen Zhang, Zhuo Li, Yuan Liu, Tao An, Giulia Gianfagna, Weikang Zheng, Guowang Du, Xing Liu, Ji-An Jiang, Johan P. U. Fynbo, Alexei S. Pozanenko, Junjie Jin, Yi Yang, Jinsong Deng, Hui Sun, Guang-Lei Wu, Yu-Hao Zhang, Bao Wang, Yu Wang, Xiangyu Wang, Bin-Bin Zhang, Yong Chen, Yonghe Zhang, Bo Wang, Xiaofeng Wang, Xuefeng Wu, Zigao Dai, Jie An, G. C. Anupama, Arvind Balasubramanian, Congying Bao, Aru Beri, Varun Bhalerao, Thomas G. Brink, Gabriele Bruni, Minxuan Cai, Zhiming Cai, Krittapas Chanchaiworawit, Yehai Chen, Huaqing Cheng, Bertrand Cordier, Chenzhou Cui, Weiwei Cui, Cuiyuan Dai, D. Eappachen, M. V. Eselevich, Xiao Fan, Zhou Fan, Yuan Fang, Hua Feng, Alexei V. Filippenko, Shaoyu Fu, He Gao, Jinjun Geng, Vitaly Goranskij, Ju Guan, Dawei Han, Jinxin Hao, Linbo He, Min He, Jingwei Hu, Maohai Huang, Shumei Jia, Ziqing Jia, Shuaiqing Jiang, Chichuan Jin, Ge Jin, Peter Jonker, E. V. Klunko, Albert K. H. Kong, Chengkui Li, Dongyue Li, Rui-Zhi Li, Wenxiong Li, Run-Duo Liang, Zhixing Ling, Congzhan Liu, Huaqiu Liu, Liangduan Liu, Xiangkun Liu, Xiaowei Liu, Yuanqi Liu, Zhengwei Liu, Fangjun Lu, Jirong Mao, Xuan Mao, A. S. Moskvitin, Haiyang Mu, Kirpal Nandra, Jan-Uwe Ness, Kangrui Ni, Kanthanakorn Noysena, Paul O'Brien, Haiwu Pan, Yu Pan. 2026-06-08. X-rays breaking out of pre-explosion ejecta mark a supernova's first light. https://arxiv.org/abs/2606.10014
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