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We report on the multi-wavelength observations of PKS 1510-089 (a flatspectrum radio quasar at z=0.361) during its high activity period between 2008September and 2009 June. During this 11 months period, the source wascharacterized by a complex variability at optical, UV and gamma-ray bands, ontime scales down to 6-12 hours. The brightest gamma-ray isotropic luminosity,recorded on 2009 March 26, was ~ 2x10^48erg s^-1. The spectrum in the Fermi-LATenergy range shows a mild curvature well described by a log-parabolic law, andcan be understood as due to the Klein-Nishina effect. The gamma-ray flux has acomplex correlation with the other wavelengths. There is no correlation at allwith the X-ray band, a weak correlation with the UV, and a significantcorrelation with the optical flux. The gamma-ray flux seems to lead the opticalone by about 13 days. From the UV photometry we estimated a black hole mass of~ 5.4x10^8 solar masses, and an accretion rate of ~ 0.5 solar masses/year.Although the power in the thermal and non-thermal outputs is smaller comparedto the very luminous and distant flat spectrum radio quasars, PKS 1510-089exhibits a quite large Compton dominance and a prominent big blue bump (BBB) asobserved in the most powerful gamma-ray quasars. The BBB was still prominentduring the historical maximum optical state in 2009 May, but the optical/UVspectral index was softer than in the quiescent state. This seems to indicatethat the BBB was not completely dominated by the synchrotron emission duringthe highest optical state. We model the broadband spectrum assuming a leptonicscenario in which the inverse Compton emission is dominated by the scatteringof soft photons produced externally to the jet. The resulting model-dependentjet energetic content is compatible with the accretion disk powering the jet,with a total efficiency within the Kerr black hole limit.

Fermi Large Area Telescope and multi-wavelength observations of the flaring activity of PKS 1510-089 between 2008 September and 2009 June