We present the results of a radio multifrequency ($\rm 3{-}340~GHz$) study of the blazar 3C 454.3. After subtracting the quiescent spectrum corresponding to optically thin emission, we found two individual synchrotron self-absorption (SSA) features in the wide-band spectrum. The one SSA had a relatively low turnover frequency (νm) in the range of $\rm 3{-}37~GHz$ (lower νm SSA spectrum, LSS), and the other one had a relatively high νm of $\rm 55{-}124~GHz$ (higher νm SSA spectrum, HSS). Using the SSA parameters, we estimated B-field strengths at the surface where optical depth τ = 1. The estimated B-field strengths were $\rm \gt 7$ and $\rm \gt 0.2~mG$ for the LSS and HSS, respectively. The LSS-emitting region was magnetically dominated before the 2014 June γ-ray flare. The quasi-stationary component (C), ∼0.6 mas apart from the 43 -GHz radio core, became brighter than the core with decreasing observing frequency, and we found that component C was related to the LSS. A decrease in jet width was found near component C. As a moving component, K14 approached component C, and the flux density of the component was enhanced while the angular size decreased. The high intrinsic brightness temperature in the fluid frame was obtained as TB, int ≈ (7.0 ± 1.0) × 1011 K from the jet component after the 2015 August γ-ray flare, suggesting that component C is a high-energy emitting region. The observed local minimum of jet width and re-brightening behaviour suggest a possible recollimation shock in component C.
We present the results of our study of cross-correlations between long-term multiband observations of the radio variability of the blazar 3C 279. More than a decade (2008–2022) of radio data were collected at seven different frequencies ranging from 2 to 230 GHz. The multiband radio light curves show variations in flux, with the prominent flare features appearing first at higher-frequency and later in lower-frequency bands. This behaviour is quantified by cross-correlation analysis, which finds that the emission at lower-frequency bands lags that at higher-frequency bands. Lag versus frequency plots are well fit by straight lines with negative slope, typically ∼−30 day GHz−1. We discuss these flux variations in conjunction with the evolution of bright moving knots seen in multiepoch Very Long Baseline Array maps to suggest possible physical changes in the jet that can explain the observational results. Some of the variations are consistent with the predictions of shock models, while others are better explained by a changing Doppler beaming factor as the knot trajectory bends slightly, given a small viewing angle to the jet.
more » « less- NSF-PAR ID:
- 10478683
- Author(s) / Creator(s):
- ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; more »
- Publisher / Repository:
- Oxford University Press
- Date Published:
- Journal Name:
- Monthly Notices of the Royal Astronomical Society
- Volume:
- 527
- Issue:
- 3
- ISSN:
- 0035-8711
- Format(s):
- Medium: X Size: p. 6970-6980
- Size(s):
- ["p. 6970-6980"]
- Sponsoring Org:
- National Science Foundation
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