Long gamma-ray bursts, which indicate the end-life collapse of very massive stars, are produced by extremely relativistic jets colliding with circumstellar medium. A huge amount of energy is released both in the first few seconds, namely the internal dissipation phase, which powers prompt emissions, and in the subsequent self-similar jet-deceleration phase, which produces afterglows observed in the broadband electromagnetic spectrum. However, prompt optical emissions of gamma-ray bursts have rarely been detected, seriously limiting our understanding of the transition between the two phases. Here we report detection of prompt optical emissions from a gamma-ray burst (that is, GRB 201223A) using a dedicated telescope array with a high temporal resolution and a wide time coverage. The early phase coincident with prompt gamma-ray emissions shows a luminosity in great excess with respect to the extrapolation of gamma-rays, while the later luminosity bump is consistent with onset of the afterglow. The clearly detected transition allows us to differentiate physical processes contributing to early optical emissions and to diagnose the composition of the jet.
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Data generated or analysed during this study are included in this Article (and its Supplementary Information). Source data are provided with this paper.
The analysis codes used to generate the data presented in this study are available from the corresponding authors upon reasonable request.
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This study is supported by the National Natural Science Foundation of China (grants 11973055, U1938201, 12133003, U1831207, U1931133) and partially supported by the Strategic Pioneer Program on Space Science, Chinese Academy of Sciences, grants XDA15052600 and XDA15016500. J. Wang is supported by the National Natural Science Foundation of China (grant 12173009) and the Natural Science Foundation of Guangxi (2020GXNSFDA238018). X.-Y.W. is supported by the National Natural Science Foundation of China under grant 12121003. Y.Y. is supported by the National Natural Science Foundation of China under grant 11873003. This work made use of data supplied by the UK Swift Science Data Centre at the University of Leicester.
The authors declare no competing interests.
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Xin, L., Han, X., Li, H. et al. Prompt-to-afterglow transition of optical emission in a long gamma-ray burst consistent with a fireball. Nat Astron 7, 724–730 (2023). https://doi.org/10.1038/s41550-023-01930-0