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

Blazars show optical and $\gamma$-ray flux variations that are generally correlated, although there are exceptions. Here we present anomalous behaviour seen in the blazar 3C 454.3 based on an analysis of quasi-simultaneous data at optical, UV, X-ray and $\gamma$-ray energies, spanning about 9 years from August 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 epochs A and B the optical and $\gamma$-ray flares are correlated, while in D and E corresponding flares in $\gamma$-rays are weak or absent. In epoch B the degree of optical polarization strongly correlates with changes in optical flux during a short-duration optical flare superimposed on one of long duration. In epoch E the optical flux and degree of polarization are anti-correlated during both the rising and declining phases of the optical flare. We carried out broad-band spectral energy distribution (SED) modeling of the source for the flaring epochs A,B, D and E, and a quiescent epoch, C. Our SED modeling indicates that optical flares with absent or weak corresponding $\gamma$-ray flares in epochs D and E could arise from changes in a combination of parameters, such as the bulk Lorentz factor, magnetic field and electron energy density, or be due to changes in the location of the $\gamma$-ray emitting regions.