Fermi view of the bright long GRB 090926A

GRB 090926A is one of the brightest long burst detected by the GBM and LAT instruments on Fermi. More than 200 photons above 100 MeV and more than 30 photons above 1 GeV with the highest energy events up to ∼20 GeV are observed after the GBM trigger (T0). The GeV emission delayed by 3 s from the onset against the low energy emission, as seen in other LAT GRBs. A sharp pulse around T0+10 s was coincidently observed by both GBM and LAT, and thus the pulse should not be due to the external shock. The spectrum exhibits an extra component against a canonical Band function from T0+3.3 to T0+21.6 s.