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A γ-ray burst with a high-energy spectral component inconsistent with the synchrotron shock model


Gamma-ray bursts are among the most powerful events in nature. These events release most of their energy as photons with energies in the range from 30 keV to a few MeV, with a smaller fraction of the energy radiated in radio, optical, and soft X-ray afterglows1. The data are in general agreement with a relativistic shock model2, where the prompt and afterglow emissions3 correspond to synchrotron radiation from shock-accelerated electrons. Here we report an observation of a high-energy (multi-MeV) spectral component in the burst of 17 October 1994 that is distinct from the previously observed lower-energy γ-ray component. The flux of the high-energy component decays more slowly and its fluence is greater than the lower-energy component; it is described by a power law of differential photon number index approximately -1 up to about 200 MeV. This observation is difficult to explain with the standard synchrotron shock model2, suggesting the presence of new phenomena such as a different non-thermal electron process, or the interaction of relativistic protons with photons at the source.

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Figure 1: Count rates for GRB941017.
Figure 2: Energy fluxes from GRB941017.


  1. 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 

  2. Mészáros, P. Theories of gamma-ray bursts. Annu. Rev. Astron. Astrophys. 40, 137–169 (2002)

    Article  ADS  Google Scholar 

  3. Costa, E. et al. Discovery of an X-ray afterglow associated with the gamma-ray burst of 28 February 1997. Nature 387, 783–785 (1997)

    Article  ADS  CAS  Google Scholar 

  4. Dingus, B. L. in High-Energy Gamma Ray Astronomy (eds Aharonian, F. A. & Völk, H. J.) 383–391 (AIP, New York, 2001)

    Google Scholar 

  5. Hurley, K. et al. Detection of a gamma-ray burst of very long duration and very high energy. Nature 372, 652–654 (1994)

    Article  ADS  CAS  Google Scholar 

  6. Atkins, R. et al. Evidence for TeV emission from GRB 970417A. Astrophys. J. 533, L119–L122 (2000)

    Article  ADS  CAS  Google Scholar 

  7. Dermer, C. D., Chiang, J. & Mitman, K. E. Beaming, baryon loading, and the synchrotron self-compton component in gamma-ray bursts. Astrophys. J. 537, 785–795 (2000)

    Article  ADS  CAS  Google Scholar 

  8. Zhang, B. & Mészáros, P. High-energy spectral components in gamma-ray burst afterglows. Astrophys. J. 559, 110–122 (2001)

    Article  ADS  CAS  Google Scholar 

  9. Katz, J. I. Delayed hard photons from gamma-ray bursts. Astrophys. J. 432, L27–L29 (1994)

    Article  ADS  CAS  Google Scholar 

  10. Harris, M. J. & Share, G. H. A Search for hard-spectrum gamma-ray bursts using SMM. Astrophys. J. 494, 724–733 (1998)

    Article  ADS  Google Scholar 

  11. Paciesas, W. S. et al. The fourth BATSE gamma-ray burst catalog (revised). Astrophys. J. Suppl. 122, 465–495 (1999)

    Article  ADS  Google Scholar 

  12. Esposito, J. A. et al. In-flight calibration of EGRET on the Compton gamma-ray observatory. Astrophys. J. Suppl. 123, 203–217 (1999)

    Article  ADS  Google Scholar 

  13. Preece, R. D. et al. The BATSE gamma-ray burst spectral catalog. I. High time resolution spectroscopy of bright bursts using high energy resolution data. Astrophys. J. Suppl. 126, 19–36 (2000)

    Article  ADS  Google Scholar 

  14. Briggs, M. S. et al. in Gamma-ray Bursts (eds Meegan, C. A., Preece, R. D. & Koshut, T. M.) 299–303 (AIP, New York, 1998)

    Google Scholar 

  15. COMPTEL burst images and time profiles. 〈〉; modified 13 August 1997.

  16. Catelli, J. R. & Dingus, B. L. in Gamma-ray Bursts (eds Meegan, C. A., Preece, R. D. & Koshut, T. M.) 309–313 (AIP, New York, 1998)

    Google Scholar 

  17. González, M. M. et al. in Gamma-Ray Burst and Afterglow Astronomy 2001 (eds Ricker, G. R. & Vanderspek, R. K.) 267–269 (AIP, New York, 2003)

    Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

  19. Thompson, D. J. et al. Calibration of the Energetic Gamma-Ray Experiment Telescope (EGRET) for the Compton Gamma-Ray Observatory. Astrophys. J. Suppl. 86, 629–656 (1993)

    Article  ADS  Google Scholar 

  20. Liang, E. & Kargatis, V. Dependence of the spectral evolution of gamma-ray bursts on their photon fluence. Nature 381, 49–51 (1996)

    Article  ADS  CAS  Google Scholar 

  21. Fishman, G. J. & Meegan, C. A. Gamma-ray bursts. Annu. Rev. Astron. Astrophys. 33, 415–458 (1995)

    Article  ADS  Google Scholar 

  22. Zhang, B. & Mészáros, P. An analysis of gamma-ray spectral break models. Astrophys. J. 581, 1236–1247 (2002)

    Article  ADS  Google Scholar 

  23. Inoue, S., Guetta, D. & Pacini, F. Precursor plerionic activity and high-energy gamma-ray emission in the supranova model of gamma-ray bursts. Astrophys. J. 583, 379–390 (2003)

    Article  ADS  Google Scholar 

  24. Vietri, M. The acceleration of ultra-high-energy cosmic rays in gamma-ray bursts. Astrophys. J. 453, 883–889 (1995)

    Article  ADS  Google Scholar 

  25. Waxman, E. Cosmological gamma-ray bursts and the highest energy cosmic rays. Phys. Rev. Lett. 75, 386–389 (1995)

    Article  ADS  CAS  Google Scholar 

  26. Alvarez-Muñiz, J., Halzen, F. & Hooper, D. W. High energy neutrinos from gamma ray bursts: Event rates in neutrino telescopes. Phys. Rev. D. 62, 093015 (2000)

    Article  ADS  Google Scholar 

  27. Boettcher, M. & Dermer, C. High-energy gamma rays from ultra-high-energy cosmic-ray protons in gamma-ray bursts. Astrophys. J. 499, L131–L134 (1998)

    Article  ADS  Google Scholar 

  28. GLAST. 〈〉; modified 29 April 2003.

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We thank M. Harris for discussions, and D. L. Bertsch for assistance with accessing the EGRET data.

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Correspondence to M. M. González.

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González, M., Dingus, B., Kaneko, Y. et al. A γ-ray burst with a high-energy spectral component inconsistent with the synchrotron shock model. Nature 424, 749–751 (2003).

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