GRB110721A was observed by the Fermi Gamma-ray Space Telescope using its two instruments the Large Area Telescope ( LAT ) and the Gamma-ray Burst Monitor ( GBM ) .
The burst consisted of one major emission episode which lasted for \sim 24.5 seconds ( in the GBM ) and had a peak flux of ( 5.7 \pm 0.2 ) \times 10 ^ { -5 } erg s ^ { -1 } cm ^ { -2 } .
The time-resolved emission spectrum is best modeled with a combination of a Band function and a blackbody spectrum .
The peak energy of the Band component was initially 15 \pm 2 MeV , which is the highest value ever detected in a GRB .
This measurement was made possible by combining GBM/BGO data with LAT Low Energy Events to achieve continuous 10 – 100 MeV coverage .
The peak energy later decreased as a power law in time with an index of -1.89 \pm 0.10 .
The temperature of the blackbody component also decreased , starting from \sim 80 keV , and the decay showed a significant break after \sim 2 seconds .
The spectrum provides strong constraints on the standard synchrotron model , indicating that alternative mechanisms may give rise to the emission at these energies .