The high-fluence GRB131108A 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 0.1 s, followed by a fainter emission detected for ~25 s with the MCAL and ~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 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+-0.2 above 30 MeV.
@article{arxiv.1407.0238,
title = {A prompt extra component in the high energy spectrum of GRB 131108A},
author = {A. Giuliani and S. Mereghetti and M. Marisaldi and F. Longo and E. Del Monte and C. Pittori and F. Verrecchia and M. Tavani and P. Cattaneo and L. Pacciani and S. Vercellone and A. Rappoldi},
journal= {arXiv preprint arXiv:1407.0238},
year = {2014}
}