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An unexpectedly rapid decline in the X-ray afterglow emission of long γ-ray bursts


‘Long’ γ-ray bursts (GRBs) are commonly accepted to originate in the explosion of particularly massive stars, which give rise to highly relativistic jets. Inhomogeneities in the expanding flow result in internal shock waves that are believed to produce the γ-rays we see1,2. As the jet travels further outward into the surrounding circumstellar medium, ‘external’ shocks create the afterglow emission seen in the X-ray, optical and radio bands1,2. Here we report observations of the early phases of the X-ray emission of five GRBs. Their X-ray light curves are characterised by a surprisingly rapid fall-off for the first few hundred seconds, followed by a less rapid decline lasting several hours. This steep decline, together with detailed spectral properties of two particular bursts, shows that violent shock interactions take place in the early jet outflows.

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Figure 1: The steep early X-ray light curves of five GRBs observed by XRT16.
Figure 2: The X-ray light curves of GRB050126 and GRB050219a as seen by BAT and XRT.
Figure 3: Evolution of the two GRB X-ray light curves from the prompt phase to the afterglow phase.

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  1. Mészáros, P. & Rees, M. Optical and long-wavelength afterglow from gamma-ray bursts. Astrophys. J. 476, 232–237 (1999)

    Article  ADS  Google Scholar 

  2. Sari, R. & Piran, T. GRB 990123: The optical flash and the fireball model. Astrophys. J. 517, L109–L112 (1999)

    Article  ADS  Google Scholar 

  3. Ford, L. A. et al. BATSE observations of gamma-ray burst spectra. 2: Peak energy evolution in bright, long bursts. Astrophys. J. 439, 307–321 (1995)

    Article  ADS  Google Scholar 

  4. Frontera, F. et al. Spectral properties of the prompt X-ray emission and afterglow from the gamma-ray burst of 1997 February 28. Astrophys. J. 439, L67–L70 (1998)

    Article  ADS  Google Scholar 

  5. Zhang, B. & Mészáros, P. Gamma-ray bursts: progress, problems, and prospects. Int. J. Mod. Phys. 19, 2385–2472 (2004)

    Article  ADS  CAS  Google Scholar 

  6. Piran, T. The physics of gamma-ray bursts. Rev. Mod. Phys. 76, 1143–1210 (2005)

    Article  ADS  Google Scholar 

  7. Piro, L. et al. Evidence for a late-time outburst of the X-ray afterglow of GRB970508 from BeppoSAX. Astron. Astrophys. 331, L41–L44 (1998)

    ADS  Google Scholar 

  8. Giblin, T. W. et al. Evidence for an early high-energy afterglow observed with BATSE from GRB 980923. Astrophys. J. 524, L47–L50 (1999)

    Article  ADS  CAS  Google Scholar 

  9. Burenin, R. A. et al. GRANAT/SIGMA observation of GRB 920723 soft gamma-ray afterglow. Astron. Astrophys. 344, L53–L56 (1999)

    ADS  Google Scholar 

  10. Piro, L. et al. Probing the environment in gamma-ray bursts: The case of an X-ray precursor, afterglow late onset and wind versus constant density profile in GRB011121 and GRB011211. Astrophys. J. 623, 314–324 (2005)

    Article  ADS  CAS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  12. Fox, D. W. et al. Discovery of early optical emission from GRB021211. Astrophys. J. 586, L5–L8 (2003)

    Article  ADS  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  14. Burrows, D. N. et al. Swift X-ray telescope and Very Large Telescope observations of the afterglow of GRB 041223. Astrophys. J. 622, L85–L88 (2005)

    Article  ADS  CAS  Google Scholar 

  15. Campana, S. et al. Swift observations of GRB050128: the early X-ray afterglow. Astrophys. J. 625, L23–L26 (2005)

    Article  ADS  CAS  Google Scholar 

  16. Burrows, D. N. et al. The Swift X-ray telescope. Space Sci. Rev. (in the press)

  17. Barthelmy, S. D. et al. The Burst Alert Telescope (BAT) on the Swift MIDEX mission. Space Sci. Rev. (in the press)

  18. Sato, G. et al. GRB050126: Bursts parameters measured by BAT. GCN Circ. 2987 (2005)

  19. Hullinger, D. et al. GRB050219: Swift-BAT detection of a burst. GCN Circ. 3038 (2005)

  20. McMahon, E., Kumar, P. & Panaitescu, A. Prompt gamma-ray and early afterglow emission in the external shock model. Mon. Not. R. Astron. Soc. 354, 915–923 (2004)

    Article  ADS  CAS  Google Scholar 

  21. Mészáros, P. & Rees, M. J. Collapsar jets, bubbles, and Fe lines. Astrophys. J. 556, L37–L40 (2001)

    Article  ADS  Google Scholar 

  22. Ramirez-Ruiz, E., Celotti, A. & Rees, M. J. Events in the life of a cocoon surrounding a light, collapsar jet. Mon. Not. R. Astron. Soc. 337, 1349–1356 (2002)

    Article  ADS  CAS  Google Scholar 

  23. Rees, M. J. & Mészáros, P. Dissipative photosphere models of gamma-ray bursts and X-ray flashes. Astrophys. J. (in the press); 〈preprint at〉 (2005)

  24. Kumar, P. & Piran, T. Energetics and luminosity function of gamma-ray bursts. Astrophys. J. 535, 152–157 (2000)

    Article  ADS  CAS  Google Scholar 

  25. Kumar, P. & Panaitescu, A. Afterglow emission from naked gamma-ray bursts. Astrophys. J. 541, L51–L54 (2000)

    Article  ADS  Google Scholar 

  26. Vietri, M. A simple, stringent test on the nature of GRB progenitors. Astropart. Phys. 14, 211–215 (2000)

    Article  ADS  Google Scholar 

  27. Roming, P. W. et al. The Swift ultra-violet/optical telescope. Space Sci. Rev. (in the press)

  28. Berger, E. et al. The discovery of the optical and near-IR afterglows of the first Swift gamma-ray bursts. Astrophys. J. (in the press); 〈preprint at〉 (2005)

  29. Schady, P. et al. GRB050219a: No Swift UVOT detection of afterglow emission. GCN Circ. 3039 (2005)

  30. Hill, J. E. et al. Read-out modes and automated operation of the Swift X-Ray telescope. Proc. SPIE 5165, 217–231 (2004)

    Article  ADS  Google Scholar 

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We acknowledge support from ASI, NASA and PPARC.

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Correspondence to G. Tagliaferri.

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Tagliaferri, G., Goad, M., Chincarini, G. et al. An unexpectedly rapid decline in the X-ray afterglow emission of long γ-ray bursts. Nature 436, 985–988 (2005).

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