  In the first week of December 2009, the blazar 3C 454.3 became the brightest
high energy source in the sky. Its photon flux reached and surpassed the level
of 1e-5 ph/cm2/s above 100 MeV. The Swift satellite observed the source several
times during the period of high gamma-ray flux, and we can construct really
simultaneous spectral energy distributions (SED) before, during, and after the
luminosity peak. Our main findings are: i) the optical, X-ray and gamma-ray
fluxes correlate; ii) the gamma-ray flux varies quadratically (or even more)
with the optical flux; iii) a simple one-zone synchrotron inverse Compton model
can account for all the considered SED; iv) in this framework the gamma-ray vs
optical flux correlation can be explained if the magnetic field is slightly
fainter when the overall jet luminosity is stronger; v) the power that the jet
spent to produce the peak gamma-ray luminosity is of the same order, or larger,
than the accretion disk luminosity. During the flare, the total jet power
surely surpassed the accretion power.
