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We analyze the behavior of the parsec-scale jet of the quasar 3C~454.3 duringpronounced flaring activity in 2005-2008. Three major disturbances propagateddown the jet along different trajectories with Lorentz factors $\Gamma>$10. Thedisturbances show a clear connection with millimeter-wave outbursts, in 2005May/June, 2007 July, and 2007 December. High-amplitude optical events in the$R$-band light curve precede peaks of the millimeter-wave outbursts by 15-50days. Each optical outburst is accompanied by an increase in X-ray activity. Weassociate the optical outbursts with propagation of the superluminal knots andderive the location of sites of energy dissipation in the form of radiation.The most prominent and long-lasting of these, in 2005 May, occurred closer tothe black hole, while the outbursts with a shorter duration in 2005 Autumn andin 2007 might be connected with the passage of a disturbance through themillimeter-wave core of the jet. The optical outbursts, which coincide with thepassage of superluminal radio knots through the core, are accompanied bysystematic rotation of the position angle of optical linear polarization. Suchrotation appears to be a common feature during the early stages of flares inblazars. We find correlations between optical variations and those at X-ray and$\gamma$-ray energies. We conclude that the emergence of a superluminal knotfrom the core yields a series of optical and high-energy outbursts, and thatthe mm-wave core lies at the end of the jet's acceleration and collimationzone.

Flaring Behavior of the Quasar 3C~454.3 across the Electromagnetic Spectrum