Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

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


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.

This is a preview of subscription content, access via your institution

Access options

Rent or buy this article

Prices vary by article type



Prices may be subject to local taxes which are calculated during checkout

Fig. 1: GRB 201223A was observed by GWAC before, during and after the GRB, providing the transition from prompt to afterglow emission and insight into the composition of GRB jets.
Fig. 2: A comparison of the prompt gamma-ray, X-ray and optical light curves of GRB 201223A measured by Swift BAT, Swift XRT, Swift UVOT, GWAC and F60A from before the event to ~104 s after the Swift trigger time.
Fig. 3: Optical and X-ray light curves of GRB 201223A and their modelling.
Fig. 4: Broadband spectra of the prompt phase in GRB 201223A.
Fig. 5: The spectral energy distribution between X-ray and optical wavelengths during the time window from 100 to 300 s after the Swift BAT trigger time.

Data availability

Data generated or analysed during this study are included in this Article (and its Supplementary Information). Source data are provided with this paper.

Code availability

The analysis codes used to generate the data presented in this study are available from the corresponding authors upon reasonable request.


  1. Zhang, B. The Physics of Gamma-Ray Bursts (Cambridge Univ. Press, 2018).

  2. Zhang, B. et al. Physical processes shaping gamma-ray burst X-ray afterglow light curves: theoretical implications from the Swift X-Ray Telescope observations. Astrophys. J. 642, 354–370 (2006).

    Article  ADS  Google Scholar 

  3. Nousek, J. A. et al. Evidence for a canonical gamma-ray burst afterglow light curve in the Swift XRT data. Astrophys. J. 642, 389–400 (2006).

    Article  ADS  Google Scholar 

  4. Vestrand, W. T. et al. A link between prompt optical and prompt γ-ray emission in γ-ray bursts. Nature 435, 178–180 (2005).

    Article  ADS  Google Scholar 

  5. Vestrand, W. T. et al. Energy input and response from prompt and early optical afterglow emission in γ-ray bursts. Nature 442, 172–175 (2006).

    Article  ADS  Google Scholar 

  6. Racusin, J. L. et al. Broadband observations of the naked-eye γ-ray burst GRB080319B. Nature 455, 183–188 (2018).

    Article  ADS  Google Scholar 

  7. Akerlof, C. et al. Observation of contemporaneous optical radiation from a γ-ray burst. Nature 398, 400–402 (1999).

    Article  ADS  Google Scholar 

  8. Vestrand, W. T. et al. The bright optical flash and afterglow from the gamma-ray burst GRB 130427A. Science 343, 38–41 (2014).

    Article  ADS  Google Scholar 

  9. Troja, E. et al. Significant and variable linear polarization during the prompt optical flash of GRB 160625B. Nature 547, 425–427 (2017).

    Article  ADS  Google Scholar 

  10. Wei, J. et al. The deep and transient Universe in the SVOM era: new challenges and opportunities—scientific prospects of the SVOM mission. Preprint at (2016).

  11. Gehrels, N. et al. The Swift gamma-ray burst mission. Astrophys. J. 611, 1005–1020 (2004).

    Article  ADS  Google Scholar 

  12. Meegan, C. et al. The Fermi Gamma-Ray Burst Monitor. Astrophys. J. 702, 791–804 (2009).

    Article  ADS  Google Scholar 

  13. Gropp, J. D. et al. GRB 201223A: Swift detection of a burst with a bright optical counterpart. GRB Coord. Netw. 29158, 1 (2020).

    Google Scholar 

  14. Wood, J. et al. GRB 201223A: Fermi GBM detection. GRB Coord. Netw. 29161, 1 (2020).

    Google Scholar 

  15. Poole, T. S. et al. Photometric calibration of the Swift ultraviolet/optical telescope. Mon. Not. R. Astron. Soc. 383, 627–645 (2008).

    Article  ADS  Google Scholar 

  16. Evans, P. A. et al. Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs. Mon. Not. R. Astron. Soc. 397, 1177–1201 (2009).

    Article  ADS  Google Scholar 

  17. Shen, R.-F. & Zhang, B. Prompt optical emission and synchrotron self-absorption constraints on emission site of GRBs. Mon. Not. R. Astron. Soc. 398, 1936–1950 (2009).

    Article  ADS  Google Scholar 

  18. Oganesyan, G., Nava, L., Ghirlanda, G., Melandri, A. & Celotti, A. Prompt optical emission as a signature of synchrotron radiation in gamma-ray bursts. Astron. Astrophys. 628, A59 (2019).

    Article  ADS  Google Scholar 

  19. Kumar, P. & Panaitescu, A. What did we learn from gamma-ray burst 080319B? Mon. Not. R. Astron. Soc. 391, L19–L23 (2008).

    ADS  Google Scholar 

  20. Li, Z. & Waxman, E. Prompt optical emission from residual collisions in gamma-ray burst outflows. Astrophys. J.Lett. 674, L65 (2008).

    Article  ADS  Google Scholar 

  21. Fan, Y.-Z., Zhang, B. & Wei, D.-M. Naked-eye optical flash from gamma-ray burst 080319B: tracing the decaying neutrons in the outflow. Phys. Rev. D 79, 021301 (2009).

    Article  ADS  Google Scholar 

  22. Woosley, S. E. & Bloom, J. S. The supernova gamma-ray burst connection. Annu. Rev. Astron. Astrophys. 44, 507–556 (2006).

    Article  ADS  Google Scholar 

  23. Chevalier, R. A. & Li, Z.-Y. Wind interaction models for gamma-ray burst afterglows: the case for two types of progenitors. Astrophys. J. 536, 195–212 (2000).

    Article  ADS  Google Scholar 

  24. Chevalier, R. A., Li, Z.-Y. & Fransson, C. The diversity of gamma-ray burst afterglows and the surroundings of massive stars. Astrophys. J. 606, 369–380 (2004).

    Article  ADS  Google Scholar 

  25. Jin, Z. P. et al. The X-ray afterglow of GRB 081109A: clue to the wind bubble structure. Mon. Not. R. Astron. Soc. 400, 1829–1834 (2009).

    Article  ADS  Google Scholar 

  26. Nugis, T. & Lamers, H. J. G. L. M. Mass-loss rates of Wolf–Rayet stars as a function of stellar parameters. Astron. Astrophys. 360, 227–244 (2000).

    ADS  Google Scholar 

  27. Langer, N. Mass-dependent mass loss rates of Wolf–Rayet stars. Astron. Astrophys. 220, 135–143 (1989).

    ADS  Google Scholar 

  28. Zhang, B. & Kobayashi, S. Gamma-ray burst early afterglows: reverse shock emission from an arbitrarily magnetized ejecta. Astrophys. J. 628, 315–334 (2005).

    Article  ADS  Google Scholar 

  29. Jin, Z. P. & Fan, Y. Z. GRB 060418 and 060607A: the medium surrounding the progenitor and the weak reverse shock emission. Mon. Not. R. Astron. Soc. 378, 1043–1048 (2007).

    Article  ADS  Google Scholar 

  30. Han, X. et al. The automatic observation management system of the GWAC network. I. System architecture and workflow. Publ. Astron. Soc. Pac. 133, 065001 (2021).

    Article  ADS  Google Scholar 

  31. Xu, Y. et al. A real-time automatic validation system for optical transients detected by GWAC. Publ. Astron. Soc. Pac. 132, 054502 (2020).

    Article  ADS  Google Scholar 

  32. Tody, D. The IRAF Data Reduction and Analysis System. Proc. SPIE 627, 733 (1986).

  33. Bessell, M. S. Standard photometric systems. Annu. Rev. Astron. Astrophys. 43, 293–336 (2005).

    Article  ADS  Google Scholar 

  34. Arnaud, K. A. XSPEC: the first ten years. In Astronomical Data Analysis Software and Systems V (eds Jacoby, G. H. & Barnes, J.) 17 (Astronomical Society of the Pacific Conference Series Vol. 101, Astronomical Society of the Pacific, 1996).

  35. Band, D. et al. BATSE observations of gamma-ray burst spectra. I. Spectral diversity. Astrophys. J. 413, 281–292 (1993).

    Article  ADS  Google Scholar 

  36. Bloom, J. S., Frail, D. A. & Sari, R. The prompt energy release of gamma-ray bursts using a cosmological k-correction. Astron. J. 121, 2879–2888 (2001).

    Article  ADS  Google Scholar 

  37. Dai, Z. G. & Lu, T. Gamma-ray burst afterglows and evolution of postburst fireballs with energy injection from strongly magnetic millisecond pulsars. Astron. Astrophys. 333, L87–L90 (1998).

    ADS  Google Scholar 

  38. Zhang, B. et al. GRB radiative efficiencies derived from the Swift data: GRBs versus XRFs, long versus short. Astrophys. J. 655, 989–1001 (2007).

    Article  ADS  Google Scholar 

  39. Beniamini, P., Nava, L. & Piran, T. A revised analysis of gamma-ray bursts’ prompt efficiencies. Mon. Not. R. Astron. Soc. 461, 51–59 (2016).

    Article  ADS  Google Scholar 

  40. Wang, X.-G. et al. How bad or good are the external forward shock afterglow models of gamma-ray bursts? Astrophys. J. Suppl. Ser. 219, 9 (2015).

    Article  ADS  Google Scholar 

  41. Li, L. et al. GRB 140423A: a case of stellar wind to interstellar medium transition in the afterglow. Astrophys. J. 900, 176 (2020).

    Article  ADS  Google Scholar 

  42. Sari, R. & Piran, T. Predictions for the very early afterglow and the optical flash. Astrophys. J. 520, 641–649 (1999).

    Article  ADS  Google Scholar 

Download references


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.

Author information

Authors and Affiliations



L.X. led the project and paper writing. H.L., L.X., J. Wang, C.W., H.C. and Y.Q. reduced and analysed the optical data. L.X., D.T., L.Z. and X.Y. analysed the high-energy data. X.H., X.L. and L.H. performed GWAC and F60A observations. B.Z., L.X., J.D., H.G. and J.R. presented the interpretation of the data and B.Z. contributed to paper writing. E.L., X.-Y.W., Z.D., X.W. and Y.Y. partially funded the facilities. J. Wei is the principal investigator for the GWAC GRB project. All authors reviewed the paper.

Corresponding authors

Correspondence to Liping Xin, Bing Zhang or Jianyan Wei.

Ethics declarations

Competing interests

The authors declare no competing interests.

Peer review

Peer review information

Nature Astronomy thanks the anonymous reviewers for their contribution to the peer review of this work.

Additional information

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figs. 1 and 2 and Table 1.

Supplementary Data 1

Data underlying Supplementary Figs. 1 and 2 and Supplementary Table 1.

Source data

Source Data Fig. 2

Data underlying Figure 2.

Source Data Fig. 3

Data underlying Figure 3.

Source Data Fig. 4

Data underlying Figure 4.

Source Data Fig. 5

Data underlying Figure 5.

Rights and permissions

Springer Nature or its licensor (e.g. a society or other partner) holds exclusive rights to this article under a publishing agreement with the author(s) or other rightsholder(s); author self-archiving of the accepted manuscript version of this article is solely governed by the terms of such publishing agreement and applicable law.

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

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).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing