Prompt spectrum of GRB 021206 supports the Cannonball Model

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.