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We report the detection by the AGILE satellite of a rapid gamma-ray flarefrom the powerful gamma-ray quasar PKS 1510-089, during a pointing centered onthe Galactic Center region from 1 March to 30 March 2008. This source has beencontinuosly monitored in the radio-to-optical bands by the GLAST-AGILE SupportProgram (GASP) of the Whole Earth Blazar Telescope (WEBT). Moreover, thegamma-ray flaring episode triggered three ToO observations by the Swiftsatellite in three consecutive days, starting from 20 March 2008. In the period1-16 March 2008, AGILE detected gamma-ray emission from PKS 1510-089 at asignificance level of 6.2-sigma with an average flux over the entire period of(84 +/- 17) x 10^{-8} photons cm^{-2} s^{-1} for photon energies above 100 MeV.After a predefined satellite re-pointing, between 17 and 21 March 2008, AGILEdetected the source at a significance level of 7.3-sigma, with an average flux(E > 100 MeV) of (134 +/- 29) x 10^{-8} photons cm^{-2} s^{-1} and a peak levelof (281 +/- 68) x 10^{-8} photons cm^{-2} s^{-1} with daily integration. Duringthe observing period January-April 2008, the source also showed an intense andvariable optical activity, with several flaring episodes and a significantincrease of the flux was observed at millimetric frequencies. Moreover, in theX-ray band the Swift/XRT observations seem to show an harder-when-brighterbehaviour of the source spectrum. The spectral energy distribution of mid-March2008 is modelled with a homogeneous one-zone synchrotron self Compton emissionplus contributions from inverse Compton scattering of external photons fromboth the accretion disc and the broad line region. Indeed, some features in theoptical-UV spectrum seem to indicate the presence of Seyfert-like components,such as the little blue bump and the big blue bump.

AGILE detection of a rapid gamma-ray flare from the blazar PKS 1510-089 during the GASP-WEBT monitoring