Abstract:
We study the core shift effect in the parsec-scale jet of the blazar 3C 454.3 using the 4.8–
36.8 GHz radio light curves obtained from three decades of continuous monitoring. From
a piecewise Gaussian fit to each flare, time lags Δt between the observation frequencies ν
and spectral indices α based on peak amplitudes A are determined. From the fit Δt ∝ ν¹̷ ᵏʳ, kᵣ = 1.10 ± 0.18 indicating equipartition between the magnetic field energy density and the particle energy density. From the fit A∝νᵅ, α is in the range −0.24 to 1.52. A mean magnetic field strength at 1 pc, B1 = 0.5 ± 0.2 G, and at the core, Bcore = 46 ± 16 mG, are inferred, consistent with previous estimates. The measure of core position offset is Ωrν = 6.4 ± 2.8 pc GHz¹̷ ᵏʳ when averaged over all frequency pairs. Based on the statistical trend shown by the measured core radius rcore as a function of ν, we infer that the synchrotron opacity model
may not be valid for all cases. A Fourier periodogram analysis yields power-law slopes in
the range −1.6 to −3.5 describing the power spectral density shape and gives bend timescales
in the range 0.52–0.66 yr. This result, and both positive and negative α, indicate that
the flares originate from multiple shocks in a small region. Important objectives met in our
study include: the demonstration of the computational efficiency and statistical basis of the
piecewise Gaussian fit; consistency with previously reported results; evidence for the core
shift dependence on observation frequency and its utility in jet diagnostics in the region close
to the resolving limit of very long baseline interferometry observations.
