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Blazars show optical and $\gamma$-ray flux variations that are generallycorrelated, although there are exceptions. Here we present anomalous behaviourseen in the blazar 3C 454.3 based on an analysis of quasi-simultaneous data atoptical, UV, X-ray and $\gamma$-ray energies, spanning about 9 years fromAugust 2008 to February 2017. We have identified four time intervals (epochs),A, B, D and E, when the source showed large-amplitude optical flares. In epochsA and B the optical and $\gamma$-ray flares are correlated, while in D and Ecorresponding flares in $\gamma$-rays are weak or absent. In epoch B the degreeof optical polarization strongly correlates with changes in optical flux duringa short-duration optical flare superimposed on one of long duration. In epoch Ethe optical flux and degree of polarization are anti-correlated during both therising and declining phases of the optical flare. We carried out broad-bandspectral energy distribution (SED) modeling of the source for the flaringepochs A,B, D and E, and a quiescent epoch, C. Our SED modeling indicates thatoptical flares with absent or weak corresponding $\gamma$-ray flares in epochsD and E could arise from changes in a combination of parameters, such as thebulk Lorentz factor, magnetic field and electron energy density, or be due tochanges in the location of the $\gamma$-ray emitting regions.

Temporal correlation between the optical and {\gamma}-ray flux variations in the blazar 3C 454.3