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

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 α ν1/kr , kr = 1.10 ± 0.18 indicating equipartition between the magnetic field energy density and the particle energy density. From the fit Aανα, 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 GHz1/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.