Prompt-to-afterglow transition of optical emission in a long gamma-ray burst consistent with a fireball

L. P. Xin, X. H. Han, Hua-Li Li, Bing Zhang, Jing Wang, D. Turpin, Xing Yang, Yulei Qiu, En‐Wei Liang, Zi-Gao Dai, Hongbo Cai, Xiaomeng Lü, Xiang‐Yu Wang, Lei Huang, Xiang-Gao Wang, Chao Wu, He Gao, Jia Ren, Lulu Zhang, Yuangui Yang, Jing-Song Deng, Jian‐Yan Wei