All Figures

$\begin{figure} \par\includegraphics[width=6.4cm,clip]{1831fg01.eps}\end{figure}$ Figure 1: Two-fluid model for relativistic outflows. A fast, relativistic ${\rm e}^{\pm }$ beam is surrounded by a slower, possibly thermal, $\rm e^{-}p$ outflow, with a mixing layer forming between the beam and the jet. The magnetic field, B, is parallel to the flow in the beam and in the mixing layer, and the field is toroidal in the jet. The magnetic lines are perturbed and the perturbation propagates outwards at the Alfvén speed, $V_{\rm A}$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.75cm,clip]{1831fg02.eps}\end{figure}$ Figure 2: Geometry of the BBH model. M₁ and M₂ denote the locations of two black holes orbiting around each other in the plane ( $\chi$ O $\zeta$ ). The coordinate system is referenced to the center of mass of the binary system (O). The accretion disk around the black hole M₁ inclined at an angle $\Omega _{\rm p}$ with respect to the orbital plane, such that the $\tilde{\xi}$ axis (parallel to the $\xi$ axis) is the precession axis. The momentary direction of the beam axis is given by the vector $\vec{M}_1 {\vec J}$ .
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{1831fg03.eps}\end{figure}$ Figure 3: Optical and radio variability of 3C 345. Shown are the epochs of spectral flares (LZ99) that have resulted in appearances of new superluminal components in the jet. The radio data are from the Michigan monitoring program (Aller et al. 2003). The optical data are from Kinman et al. (1968); Smyth & Wolstencroft (1970); Lü (1972); McGimsey et al. (1975); Pollock et al. (1979); Angione et al. (1981); Kidger (1988) Webb et al. (1988); Kidger & de Diego (1990); Vio et al. (1991); Schramm et al. (1993); Babadzhanyants et al. (1995); Belokon' & Babadzhanyants (1999). All optical data have been converted into the B magnitude scale.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{1831fg04.eps}\end{figure}$ Figure 4: Parsec-scale jet in 3C 345 at 5 and 15 GHz. Contours are drawn at -1, 1, $\sqrt {2}$ , 2, ... of the lowest contour (2.5 mJy/beam, in both images). Curved lines mark the trajectories of superluminal features C1-C7 identified in the jet. The component trajectories are polynomial fits to the position measurements from the 1979-1998 VLBI monitoring data (ZCU95; L96; R00). The positions of C7 measured at 22 GHz are shown in the inset.
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In the text

$\begin{figure} \par\includegraphics[width=12cm,clip]{1831fg05.eps}\end{figure}$ Figure 5: Kinematic properties of the jet determined from the observed trajectory of C7. In all panels, the solid line represents a model with $\Gamma _{{\rm C7}}$ increasing linearly with time from $\Gamma _{{\rm C7}}=2.2$ in 1990 to $\Gamma _{{\rm C7}}=10.6$ in 1998. The lower boundary of the shaded area corresponds to $\Gamma _{{\rm C7}}= \Gamma _{{\rm min}} = (\beta _{{\rm app}}^2+1)^{1/2}$ , the upper boundary is drawn for $\Gamma _{{\rm C7}}=11$ . Arrows indicate the direction of increasing $\Gamma _{{\rm C7}}$ from $\Gamma _{{\rm min}}$ to 11. Individual panels show: a) Measured apparent speed $\beta _{{\rm app}}$ (dashed line) and evolution of the Lorentz factor $\Gamma _{\rm j}$ . b) Angle between the velocity vector of C7 and the line of sight. c) Doppler factor. d) Distance travelled by C7 in the rest frame of the jet. The derived $R_{{\rm trav}} > \beta _{{\rm C7}} \Delta t_{{\rm obs}}$ because of the time contraction in the observer's frame of reference.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{1831fg06.eps}\end{figure}$ Figure 6: Apparent acceleration ${\rm d}\mu /{\rm d}\Theta _{{\rm app}}$ of the component proper motions, plotted versus the component epochs of origin. The origin epochs are obtained by back-extrapolating the observed trajectories of the jet components (L96). The shaded area cover the range of precession periods which would reproduce the observed trend of ${\rm d}\mu /{\rm d}\Theta _{{\rm app}}$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.7cm,clip]{1831fg07.eps}\end{figure}$ Figure 7: Position angle of different jet components measured at 22 GHz at 0.5 mas separation from the core. Short-term variations, with a period of $\approx$ 9.5 years, are evident. A linear regression (dotted line) suggests the presence of a long-term trend, with a annual change rate of 0.4 $\pm$ 0.3 $\hbox {$^\circ $ }$ /year. The shaded area shows the best fit by the two periodical processes combined, with the estimated periods $P_{{\rm short}} = 9.5$ $\pm$ 0.1 years and $P_{{\rm long}} = 1600$ $\pm$ 1300 years. The solid line represents the trend in the position angle due to the long-term periodicity.
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In the text

$\begin{figure} \par\includegraphics[width=8.2cm,clip]{1831fg08.eps}\end{figure}$ Figure 8: Composition of a nuclear flare. The flare begins with an injection of highly energetic particles emitting optical synchrotron radiation. The timescale of the injection $\Delta \tau _{{\rm opt}}$ is comparable to the synchrotron loss time of the optically emitting plasma. Rapid energy losses and injection of radio emitting plasma on the timescale $\Delta \tau _{{\rm rad}}$ lead to progressively decreasing mean energy of the plasma and subsequent propagation of the flare to radio wavelengths. The optically emitting plasma is represented in the model by a point-like component injected into the beam, while the radio emitting plasma is temporally resolved, with the resulting $\Delta \tau _{{\rm opt}} < 0.01\Delta \tau _{{\rm rad}}$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{1831fg09.eps}\end{figure}$ Figure 9: Rest frame time recovered from the precession fit (describing the trajectory of the VLBI component) and the BBH models 1 and 2 (describing the optical variability) under the consistency constraints discussed in Sect. 4.4. The injection epoch $t_{{\rm inj}}=1991.05$ (for which $t_{{\rm rest}}=0$ is required by the precession fit) is reproduced by the BBH model 1 and cannot be recovered from the BBH model 2. The agreement between the precession fit and model 1 ensures that the BBH scenario provides a single framework for describing simultaneously the observed trajectory and flux density changes of C7 and the observed variability of the optical emission of 3C 345.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{1831fg10.eps}\end{figure}$ Figure 10: Evolution of the separation of the jet component C7 from the core. The fit by the precession model is consistent with the fit by BBH model 1. BBH model 2 fails to reproduce the earliest position measurements of C7.
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In the text

$\begin{figure} \par\includegraphics[width=7.25cm,clip]{1831fg11.eps}\end{figure}$ Figure 11: Radio flux density of C7 at 22 GHz. The fits by the precession model and BBH model 1 are consistent. BBH model 2 cannot reproduce the onset of the radio emission.
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In the text

$\begin{figure} \par\includegraphics[width=7.65cm,clip]{1831fg12.eps}\end{figure}$ Figure 12: Apparent speed evolution of the jet component C7 recovered from the precession and BBH fits. The fit by BBH model 1 is consistent with the fit by the precession, while BBH model 2 cannot be reconciled with the precession fit at all.
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In the text

$\begin{figure} \par\includegraphics[width=6.9cm,clip]{1831fg13.eps}\end{figure}$ Figure 13: Two-dimensional path of C7. The precession fit and the fit by BBH model 1 are presented.
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In the text

$\begin{figure} \par\includegraphics[width=7.2cm,clip]{1831fg14.eps}\end{figure}$ Figure 14: Two-dimensional path of C7 within 1 mas of the nucleus. The difference between the precession and BBH model 1 fit is due to the orbital motion of the black hole ejecting the jet.
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In the text

$\begin{figure} \par\includegraphics[width=7.6cm,clip]{1831fg15.eps}\end{figure}$ Figure 15: Optical variability in 3C 345 in 1990-93. Solid lines show the fits by the BBH model. Individual peaks result from the orbital motion in the BBH system.
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{1831fg16.eps}\end{figure}$ Figure 16: Range of acceptable solutions for the mass M₁ of the primary black hole in 3C 345. The acceptable solutions exist within the range 7.1 $\times$ $10^8~{M}_{\odot} \le M_1 \le 7.5\times 10^8~{M}_{\odot}$ . Asterisks mark the solution for $\mu _{{\rm 1,2}} = 1$ , for which M₁ = M₂ = 7.1 $\times$ $10^8~{M}_{\odot}$ . Shaded areas cover the values of M₁, $T_{\rm o}$ and $\mu _{1,2}$ for which the accretion disk cannot remain stable over the typical timescale of existence of a powerful radio source in AGN, $\tau _{{\rm agn}}\le 10^8$ yr.
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In the text

$\begin{figure} \par\includegraphics[width=7.75cm,clip]{1831fg17.eps}\end{figure}$ Figure 17: Characteristic timescales of disk activity in 3C 345, compared to the quasi-period of the nuclear flares and to the orbital and characteristic disk rotation periods). The disk thermal instability operates at $t\sim 4$ yr at distances of $\sim$ $20~R_{\rm G}$ . The mechanical (sound wave) instability reaches the same timescale at $\sim$ $200~R_{\rm G}$ , where it becomes comparable with the orbital and drift (accretion rate variations) timescales of the disk. A combination of these effects may cause the flare activity observed in 3C 345.
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{1831fg10.eps}\end{figure}$	Figure 10: Evolution of the separation of the jet component C7 from the core. The fit by the precession model is consistent with the fit by BBH model 1. BBH model 2 fails to reproduce the earliest position measurements of C7.
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$\begin{figure} \par\includegraphics[width=7.25cm,clip]{1831fg11.eps}\end{figure}$	Figure 11: Radio flux density of C7 at 22 GHz. The fits by the precession model and BBH model 1 are consistent. BBH model 2 cannot reproduce the onset of the radio emission.
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$\begin{figure} \par\includegraphics[width=7.65cm,clip]{1831fg12.eps}\end{figure}$	Figure 12: Apparent speed evolution of the jet component C7 recovered from the precession and BBH fits. The fit by BBH model 1 is consistent with the fit by the precession, while BBH model 2 cannot be reconciled with the precession fit at all.
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$\begin{figure} \par\includegraphics[width=6.9cm,clip]{1831fg13.eps}\end{figure}$	Figure 13: Two-dimensional path of C7. The precession fit and the fit by BBH model 1 are presented.
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$\begin{figure} \par\includegraphics[width=7.2cm,clip]{1831fg14.eps}\end{figure}$	Figure 14: Two-dimensional path of C7 within 1 mas of the nucleus. The difference between the precession and BBH model 1 fit is due to the orbital motion of the black hole ejecting the jet.
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$\begin{figure} \par\includegraphics[width=7.6cm,clip]{1831fg15.eps}\end{figure}$	Figure 15: Optical variability in 3C 345 in 1990-93. Solid lines show the fits by the BBH model. Individual peaks result from the orbital motion in the BBH system.
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