FERMI-LAT OBSERVATIONS OF THE 2014 MAY-JULY OUTBURST FROM 3C 454.3

A prominent outburst of the flat spectrum radio quasar 3C 454.3 was observed in 2014 June with the Fermi Large Area Telescope. This outburst was characterized by a three-stage light-curve pattern-plateau, flare, and post-flare-that occurred from 2014 May to July, in a similar pattern as observed during the exceptional outburst in 2010 November. The highest flux of the outburst reported in this paper occurred during 2014 June 7-29, showing a multiple-peak structure in the light-curves. The average flux in these 22 days was found to be F[E > 100 MeV] = (7.2 +/- 0.2) x 10(-6) ph cm(-2) s(-1), with a spectral index, for a simple power law, of Gamma = 2.04 +/- 0.01. That made this outburst the first gamma-ray high state of 3C 454.3 ever to be detected by Fermi with such a hard spectrum over several days. The highest flux was recorded on 2014 June 15, in a 3 hr bin, at MJD 56823.5625, at a level of F[E > 100 MeV] = (17.6 +/- 1.9) x 10(-6) ph cm(-2) s(-1). The rise time of one of the short subflares was found to be T-r = 1200 +/- 700 s at MJD. =. 56827, when the flux increased from 4 to 12 x 10(-6) ph cm(-2) s(-1). Several photons above 20 GeV were collected during this outburst, including one at 45 GeV on MJD 56827, constraining the gamma-ray emission region to be located close to the outer boundary of the broad-line region, leading to fast flux variability.