Agile detection of a strong gamma-ray flare from the blazar 3C 454.3

We report the first blazar detection by AGILE. AGILE detected 3C 454.3 during a period of strongly enhanced optical emission in 2007 July. AGILE observed the source with a dedicated repointing during the period 2007 July 24-30 with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV to 50 GeV and 18-60 keV ranges, respectively. Over the entire period, AGILE detected gamma-ray emission from 3C 454.3 at a significance level of 13.8 sigma with an average flux (E > 100 MeV) of (280 +/- 40) x 10(-8) photons cm(-2) s(-1). The gamma-ray flux appears to be variable toward the end of the observation. No emission was detected by Super-AGILE in the energy range 20-60 keV, with a 3 sigma upper limit of 2.3 x 10(-3) photons cm(-2) s(-1). The gamma-ray flux level of 3C 454.3 detected by AGILE is the highest ever detected for this quasar and among the most intense gamma-ray sluxes ever detected from flat-spectrum radio quasars.