The high-fluence GRB 131108A at redshift z=2.4 , was detected by the Mini-Calorimeter ( MCAL , 0.35–100 MeV ) and the Gamma-Ray Imaging Detector ( GRID , 30 MeV – 30 GeV ) onboard the AGILE satellite .
The burst emission consisted of a very bright initial peak , lasting \sim 0.1 s , followed by a fainter emission detected for \sim 25 s with the MCAL and \sim 80 s with the GRID .
The AGILE spectra , when compared with those reported at lower energies , indicate the presence of a prominent high-energy component with peak energy in the \sim 10–20 MeV region .
Contrary to other GRBs , this high-energy component is present also during the initial peak , with power law photon index of about –1.6 below 10 MeV and –2.35 \pm 0.2 above 30 MeV .