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We study the core shift effect in the parsec scale jet of the blazar 3C 454.3using the 4.8 GHz - 36.8 GHz radio light curves obtained from three decades ofcontinuous monitoring. From a piecewise Gaussian fit to each flare, time lags$\Delta t$ between the observation frequencies $\nu$ and spectral indices$\alpha$ based on peak amplitudes $A$ are determined. From the fit $\Delta t\propto \nu^{1/k_r}$, $k_r = 1.10 \pm 0.18$ indicating equipartition betweenthe magnetic field energy density and the particle energy density. From the fit$A \propto \nu^\alpha$, $\alpha$ is in the range $-0.24$ to $1.52$. A meanmagnetic field strength at 1 pc, $B_1 = 0.5 \pm 0.2$ G, and at the core,$B_{\rm core} = 46 \pm 16$ mG, are inferred, consistent with previousestimates. The measure of core position offset is $\Omega_{r\nu} = 6.4 \pm 2.8$pc GHz$^{1/k_r}$ when averaged over all frequency pairs. Based on thestatistical trend shown by the measured core radius $r_{\rm core}$ as afunction of $\nu$, we infer that the synchrotron opacity model may not be validfor all cases. A Fourier periodogram analysis yields power law slopes in therange $-1.6$ to $-3.5$ describing the power spectral density shape and givesbend timescales in the range $0.52 - 0.66~$yr. This result, and both positiveand negative $\alpha$, indicate that the flares originate from multiple shocksin a small region. Important objectives met in our study include: thedemonstration of the computational efficiency and statistical basis of thepiecewise Gaussian fit; consistency with previously reported results; evidencefor the core shift dependence on observation frequency and its utility in jetdiagnostics in the region close to the resolving limit of very long baselineinterferometry observations.

Frequency dependent core shifts and parameter estimation for the blazar 3C 454.3