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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.


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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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The authors declare that they have no competing financial interests.

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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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