Fermi-LAT Observation of 3C 454.3 during its 2014 May-July outburst

Flat Spectrum Radio Quasar 3C 454.3 is the brightest active galactic nucleus to have been detected in the γ-ray spectral band. It was observed in an outburst phase during 2014 May-July, and a large amount of data was collected with the Fermi-Large Area Telescope (Fermi-LAT) from 100 MeV to several tens of GeV. In its nominal sky-survey operating mode, Fermi-LAT can see the whole sky every 3 hours, which allowed us to draw detailed light curves during its flaring period, and perform spectral analysis during some specific sub-flares. During these periods, we observed the following features: A fast variability; a hard spectral index close to G = 2:0, by fitting spectral energy distributions with a single power law model > 100 MeV; the highest flux at a level of F[E>100 MeV] = 21.6 ±2:6×10^-6photons cm^-2 s^-; several photons at high energies beyond 20 GeV.We will present upper limits on the estimation of the Doppler factor d and discuss constraints on the location of the γ-ray emitting region.