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.

Energy input and response from prompt and early optical afterglow emission in γ-ray bursts


The taxonomy of optical emission detected during the critical first few minutes after the onset of a γ-ray burst (GRB) defines two broad classes: prompt optical emission correlated with prompt γ-ray emission1, and early optical afterglow emission uncorrelated with the γ-ray emission2. The standard theoretical interpretation attributes prompt emission to internal shocks in the ultra-relativistic outflow generated by the internal engine3,4,5; early afterglow emission is attributed to shocks generated by interaction with the surrounding medium6,7,8. Here we report on observations of a bright GRB that, for the first time, clearly show the temporal relationship and relative strength of the two optical components. The observations indicate that early afterglow emission can be understood as reverberation of the energy input measured by prompt emission. Measurements of the early afterglow reverberations therefore probe the structure of the environment around the burst, whereas the subsequent response to late-time impulsive energy releases reveals how earlier flaring episodes have altered the jet and environment parameters. Many GRBs are generated by the death of massive stars that were born and died before the Universe was ten per cent of its current age9,10, so GRB afterglow reverberations provide clues about the environments around some of the first stars.

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

Figure 1: The onset of prompt optical emission from GRB 050820a.
Figure 2: A comparison of the early optical light curve and the γ-ray light curve measured for GRB 050820a.
Figure 3: The decomposition the optical light curve measured for GRB 050820a into primary optical components.
Figure 4: Broadband spectra of prompt emission from GRB 050820a.


  1. 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  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  3. Fenimore, E. E., Madras, C. D. & Nayakshin, S. Expanding relativistic shells and gamma-ray burst temporal structure. Astrophys. J. 473, 998–1012 (1996)

    Article  ADS  Google Scholar 

  4. Meszaros, P. & Rees, M. GRB 990123: reverse and internal shock flashes and late afterglow behaviour. Mon. Not. R. Astron. Soc. 306, L39–L43 (1999)

    Article  ADS  Google Scholar 

  5. Katz, J. Low-frequency spectra of gamma-ray bursts. Astrophys. J. 432, L107–L109 (1994)

    Article  ADS  Google Scholar 

  6. Meszaros, P. & Rees, M. Optical and long-wavelength afterglow from gamma-ray bursts. Astrophys. J. 476, 232–237 (1997)

    Article  ADS  Google Scholar 

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

    Article  ADS  Google Scholar 

  8. Panaitescu, A. & Kumar, P. Analysis of two scenarios for the early optical emission of the gamma-ray burst afterglow 990123 and 021211. Mon. Not. R. Astron. Soc. 353, 511–522 (2004)

    Article  ADS  CAS  Google Scholar 

  9. Lamb, D. Q. & Reichart, D. E. Gamma-ray bursts as a probe of the very high redshift universe. Astrophys. J. 536, 1–18 (2000)

    Article  ADS  Google Scholar 

  10. Ciardi, B. & Loeb, A. Expected number and flux distribution of gamma-ray burst afterglows with high redshifts. Astrophys. J. 540, 687–696 (2005)

    Article  ADS  Google Scholar 

  11. Page, M. et al. GRB 050820: Swift detection of a GRB. GRB Circ. Netw. 3830 (2005)

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

    Article  ADS  CAS  Google Scholar 

  13. Vestrand, W. T. et al. The RAPTOR experiment: a system for monitoring the optical sky in real time. Proc. SPIE 4845, 126–136 (2002)

    Article  ADS  Google Scholar 

  14. Wren, J. et al. GRB050820: Early RAPTOR detections. GRB Circ. Netw. 3836 (2005)

  15. Van Paradijs, J., Kouveliotou, C. & Wijers, R. A. M. J. Gamma ray burst afterglows. Annu. Rev. Astron. Astrophys. 38, 379–425 (2000)

    Article  ADS  CAS  Google Scholar 

  16. Li, W. et al. The early light curve of the optical afterglow of GRB 021211. Astrophys. J. 586, L9–L12 (2003)

    Article  ADS  Google Scholar 

  17. Fox, D. W. et al. Early optical emission from the γ-ray burst of 4 October 2002. Nature 422, 284–286 (2003)

    Article  ADS  CAS  Google Scholar 

  18. Wozniak, P. R. et al. RAPTOR observations of the early optical afterglow from GRB 050319. Astrophys. J. 627, L13–L16 (2005)

    Article  ADS  CAS  Google Scholar 

  19. Rykoff, E. S. et al. The early optical afterglow of GRB 030418 and progenitor mass loss. Astrophys. J. 601, 1013–1018 (2004)

    Article  ADS  Google Scholar 

  20. Chester, M. et al. Swift/UVOT photometry of GRB 050820. GRB Circ. Netw. 3838 (2005)

  21. Page, K. L. et al. GRB 050820: refined XRT analysis. GRB Circ. Netw. 3837 (2005)

  22. Lazzati, D. & Begelman, M. Thick fireballs and the steep decay in the early X-ray afterglow of gamma-ray bursts. Astrophys. J. 641, 972–977 (2006)

    Article  ADS  CAS  Google Scholar 

  23. Quimby, R. M. et al. Early-time observations of the GRB 050319 optical transient. Astrophys. J. 640, 402–406 (2006)

    Article  ADS  CAS  Google Scholar 

  24. Falcone, A. D. et al. The giant x-ray flare of GRB 050502b: evidence for late-time internal engine activity. Astrophys. J. 641, 1010–1017 (2006)

    Article  ADS  CAS  Google Scholar 

  25. Wozniak, P. R. et al. RAPTOR observations of delayed explosive activity in the high-redshift gamma-ray burst GRB 060206. Astrophys. J. 642, L99–L102 (2006)

    Article  ADS  CAS  Google Scholar 

  26. Fox, D. B. & Cenko, S. B. GRB 050820: Optical afterglow from P60. GRB Circ. Netw. 3829 (2005)

  27. Prochaska, J. X. et al. GRB 050820: High resolution spectroscopy from Keck. GRB Circ. Netw. 3833 (2005)

  28. Ledoux, C. et al. VLT/UVES spectroscopy of GRB050820. GRB Circ. Netw. 3869 (2005)

  29. Golenetskii, S. et al. GRB050820a—a very long GRB like GRB041219a? Konus-Wind Observation. GRB Circ. Netw. 3852 (2005)

Download references


The RAPTOR project is supported by the Laboratory Directed Research and Development program at Los Alamos National Laboratory. The Konus-Wind experiment is supported by the Russian Space Agency and the Russian Foundation for Basic Research.

Author information

Authors and Affiliations


Corresponding author

Correspondence to W. T. Vestrand.

Ethics declarations

Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

Rights and permissions

Reprints and permissions

About this article

Cite this article

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

Download citation

  • Received:

  • Accepted:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


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