  The quasar 3C 454.3 is a blazar known for its rapid and violent outbursts
seen across the electromagnetic spectrum. Using gamma-ray, X-ray, multi-band
optical, and very long baseline interferometric data we investigate the nature
of two such events that occurred in 2013 and 2014 accompanied by strong
variations in optical polarization, including a 230 degree electric vector
position angle (EVPA) rotation. Our results suggest that a single disturbance
was responsible for both flaring events. We interpret the disturbance as a
shock propagating down the jet. Under this interpretation the 2013-flare
originated most likely due to changes in the viewing angle caused by perhaps a
bent or helical trajectory of the shock upstream of the radio core. The
2014-flare and optical polarization behavior are the result of the shock
exiting the 43 GHz radio core, suggesting that shock crossings are one of the
possible mechanisms for EVPA rotations.
