GRB 021206 is one of the brightest GRBs ever observed. Its prompt emission, as measured by RHESSI, shows an unexpected spectral hardening around 5 MeV. Below this energy, the spectrum is well described by a Band function with a peak energy of about 700 keV. However, using the full RHESSI energy range up to 17 MeV, the spectrum can not be fitted with a Band function. The Cannonball Model on the other hand predicts such a spectral hardening, and we found that it fits the spectrum of GRB 021206 perfectly.
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