Annu. Rev. Astron. Astrophys. 1997. 35: 607-36
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3.2. Curved Trajectories

Figure 8 shows the different apparent trajectories (in the region 1 milliarcsec from the core) of the superluminal features of 3C 345 (JA Zensus, AP Lobanov, KJ Leppänen, SC Unwin, and AE Wehrle, in preparation), as measured with respect to the stationary core D (Bartel et al 1986). These tracks are substantially curved and show kinks and bends. Note that at larger distances from the core, the components appear to roughly follow the same curved trajectory in the northwest direction towards the arcsecond structure; near the core the trajectories differ significantly. Note that in this and other sources, the curvature appears most pronounced near the core - reflected in bends and wiggles with amplitudes of < 0.2-0.5 milliarcsec. There should also be opacity effects causing frequency dependency of component shapes and positions and of the observed trajectories. Such behavior is seen, for example, in 3C 345 and also in 4C 39.25 (Alberdi et al 1997).

Figure 8

Figure 8. The trajectories of superluminal features in 3C 345 within 1 milliarcsec from the core are shown (JA Zensus, AP Lobanov, KJ Leppänen, SC Unwin, and AE Wehrle, in preparation), measured with respect to the core D. Lines are from polynomial fits to x and y coordinates in time.

Similar curved trajectories or jet ridge lines have been reported in a growing number of cases, especially from high-resolution observations at millimeter wavelengths (Krichbaum et al 1994b, Bääth 1994, Krichbaum et al 1994a). The BL Lac object 1803+784 shows quasisinusoidal curvature in a parsec-scale jet (Krichbaum et al 1994b). The extrema in apparent velocity occur at or near the turning points in the curvature.

IIK Pauliny-Toth (personal communication) finds from observations during 1983-1990 that the jet in the quasar 3C 454.3 is curved, which is confirmed by observations at 3 mm (Krichbaum et al 1995). A correlation between curvature and velocity changes is also observed in 3C 84 (Krichbaum et al 1993a, c) at high frequencies, with components accelerating from < 0.1 to ~ 0.5 h-1 c (see also Romney et al 1995, Dhawan et al 1997, and references therein). In 3C 273, it is not clear if all components follow the same path, although at least two component pairs have indistinguishable trajectories within the bent jet (Krichbaum et al 1993a, Abraham et al 1996).

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