Can long-term periodic variability and jet helicity in 3C 120 be explained by jet precession?

Abstract

Optical variability of 3C 120 is discussed in the framework of jet precession. Specifically, we assume that the observed long‐term periodic variability is produced by the emission from an underlying jet with a time‐dependent boosting factor driven by precession. The differences in the apparent velocities of the different superluminal components in the milliarcsec jet can also be explained by the precession model as being related to changes in the viewing angle. The evolution of the jet components has been used to determine the parameters of the precession model, which also reproduce the helical structure seen at large scales. Among the possible mechanisms that could produce jet precession, we consider that 3C 120 harbours a supermassive black hole binary system in its nuclear region, and that torques induced by misalignment between the accretion disc and the orbital plane of the secondary black hole are responsible for this precession; we estimate upper and lower limits for the black holes masses and their mean separation.

Faraday rotation in jets of AGN: the case of 3C 120

“…components in the 2007 jet do not travel across the localized region of enhanced RM, failing to reveal it, since it is only through the motion of superluminal components that we are able to map the jet polarization owing to the increase in energy density and magnetic field ordering that they produce. The rotation of the direction of ejection is in agreement with the helical structure suggested by [22], and the proposed precessing/helical models of [23] and [24]. In particular, [23] estimated a precession period of 12.3 yr, predicting a swing to the north of the direction of ejection in the jet between our 2001 and 2007 epochs, as is indeed observed.…”

The Connection between the Radio Jet and the γ-ray Emission in the Radio Galaxy 3C 120 and the Blazar CTA 102

“…This progressive slowdown in the apparent velocity of components could be explained by a change in the velocity and/or a change in the orientation of the components. A precession model for 3C 120 has been already proposed by [12] as well as by [13]. Interestingly, in [13], the authors interpreted the γ-ray event in September 2014 considering the jet as formed by a fast spine and a slower outer layer, where it is only the spine that changes its direction and occasionally points more toward the observer, as during γ-ray flares.…”

Tracing the merger-driven evolution of active galaxies using the CJF sample

“…A BBH system may produce a precessing jet base (e.g., Yokosawa & Inoue 1985;Romero et al 2003;Roland et al 2008;Kaastra & Roos 1992) and thus a bent jet. The detected periodicities in the light curves may also be caused by a BBH (e.g., Lehto & Valtonen 1996;Sillanpaa et al 1988;Qian et al 2007;Caproni & Abraham 2004). Finally, there is a number of more indirect evidence possibly connected to these systems (e.g., Komossa 2006).…”

“…For references, see Table 12. Caproni & Abraham (2004) We note here the ambiguity of the classification of sources into the different pre-merger stages (Table 9). Starburst activity is the defining, although not unambiguous, property of identifying systems that are currently undergoing a merger, the alternative evidence discussed above being a weaker selection criteria.…”

“…Precession of the jet has been employed to explain a variety of phenomena including the variability that AGN show at different wavelengths (e.g., Caproni & Abraham 2004;Roland et al 1994). An intrinsically helical jet can also exhibit the same morphological and kinematical results (for a study of the different kind of helicities in AGN jets, see Steffen 1997).…”