AGILE detection of intense gamma-ray emission from the blazar PKS 1510-089

Context We report the detection by the AGILE (Astro-rivelatore Gamma a Immagini LEggero) satellite of an intense gamma-ray flare from the source AGL J1511-0909, associated with the powerful quasar PKS 1510-089, during ten days of observations from 23 August to 1 September 2007. <BR />Aims During the observation period, the source was in optical decrease following a flaring event monitored by the GLAST-AGILE Support Program (GASP) of the Whole Earth Blazar Telescope (WEBT). The simultaneous gamma-ray, optical, and radio coverage allows us to study the spectral energy distribution and the theoretical models based on the synchrotron and inverse Compton (IC) emission mechanisms. <BR />Methods AGILE observed the source with its two co-aligned imagers, the Gamma-Ray Imaging Detector and the hard X-ray imager Super-AGILE sensitive in the 30 MeV div 50 GeV and 18 div 60 keV bands, respectively. <BR />Results Between 23 and 27 August 2007, AGILE detected gamma-ray emission from PKS 1510-089 when this source was located 50 off-axis, with an average flux of (270 65) 10<SUP>-8</SUP> photons cm<SUP>-2</SUP> s<SUP>-1</SUP> for photon energy above 100 MeV. In the following period, 28 August-1 September, after a satellite re-pointing, AGILE detected the source at 35 off-axis, with an average flux (E > 100 MeV) of (195 30) 10<SUP>-8</SUP> photons cm<SUP>-2</SUP> s<SUP>-1</SUP>. No emission was detected by Super-AGILE, with a 3-sigma upper limit of 45 mCrab in 200 ks. <BR />Conclusions The spectral energy distribution is modelled with a homogeneous one-zone synchrotron self Compton (SSC) emission plus contributions by external photons the SSC emission contributes primarily to the X-ray band, whereas the contribution of the IC from the external disc and the broad line region match the hard gamma-ray spectrum observed.