Kinematics of the parsec-scale radio jet in 3C 48
An, T.; Hong, X.Y.; Hardcastle, M.J.; Worrall, D.M.; Venturi, T.; Pearson, T.J.; Shen, Z.Q.; Zhao, W.; Feng, W.X.
Citation: An , T , Hong , X Y , Hardcastle , M J , Worrall , D M , Venturi , T , Pearson , T J , Shen , Z Q , Zhao , W & Feng , W X 2010 , ' Kinematics of the parsec-scale radio jet in 3C 48 ' Monthly Notices of the Royal Astronomical Society , vol 402 , no. 1 , pp. 87-104 .
We present results on the compact steep-spectrum quasar 3C 48 from observations with the Very Long Baseline Array (VLBA), the Multi-Element Radio Linked Interferometer Network (MERLIN) and the European Very long baseline interferometry (VLBI) Network (EVN) at multiple radio frequencies. In the 1.5-GHz VLBI images, the radio jet is characterized by a series of bright knots. The active nucleus is embedded in the southernmost VLBI component A, which is further resolved into two sub-components A1 and A2 at 4.8 and 8.3 GHz, respectively. A1 shows a flat spectrum and A2 shows a steep spectrum. The most strongly polarized VLBI components are located at component C ∼ 0.25 arcsec north of the core, where the jet starts to bend to the north-east. The polarization angles at C show gradual changes across the jet width at all observed frequencies, indicative of a gradient in the emission-weighted intrinsic polarization angle across the jet and possibly a systematic gradient in the rotation measure; moreover, the percentage of polarization increases near the curvature at C, likely consistent with the presence of a local jet–interstellar-medium interaction and/or changing magnetic-field directions. The hot spot B shows a higher rotation measure, and has no detected proper motion. These facts provide some evidence for a stationary shock in the vicinity of B. Comparison of the present VLBI observations with those made 8.43 yr ago suggests a significant northward motion for A2 with an apparent transverse velocity βapp= 3.7 ± 0.4c . The apparent superluminal motion suggests that the relativistic jet plasma moves at a velocity of ≳0.96c if the jet is viewed at an inclination angle less than 20° . A simple precessing jet model and a hydrodynamical isothermal jet model with helical-mode Kelvin–Helmholtz instabilities are used to fit the oscillatory jet trajectory of 3C 48 defined by the bright knots
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