View metadata, citation and similar papers at core.ac.uk brought to you by CORE Astron. Astrophys. 360, 57–64 (2000) providedASTRONOMY by Servicio de Difusión de la Creación Intelectual AND ASTROPHYSICS Beaming and precession in the inner jet of 3C 273 II. The central engine G.E. Romero1,?, L. Chajet2, Z. Abraham3, and J.H. Fan4 1 Instituto Argentino de Radioastronom´ıa, C.C.5, (1894) Villa Elisa, Bs. As., Argentina 2 Facultad de Ciencias Astronomicas´ y Geof´ısicas, UNLP, Paseo del Bosque, 1900 La Plata, Argentina 3 Universidade de Sao˜ Paulo, Instituto Astronomicoˆ e Geof´ısico, Av. M. Stefano 4200, CEP 04301-904 Sao˜ Paulo, SP, Brazil 4 Guangzhou Normal University, Center for Astrophysics, Guangzhou 510400, P.R. China Received 29 December 1999 / Accepted 25 May 2000 Abstract. The quasar 3C 273 is a well-known superluminal Recently, Abraham & Romero (1999, hereafter Paper I) have source. More than 10 radio components have been detected used all available VLBI data of superluminal components in moving away from the nucleus with different superluminal 3C 273 to determine the kinematic evolution of the inner jet. speeds and position angles. The pattern of ejection suggests the They have shown that the different velocities and position angles existence of a precessing inner jet, whose kinematics has been at the ejection time of the various well-monitored components discussed by Abraham & Romero (1999). We now present a are consistent with the existence of a precessing inner jet in the binary black hole model for the central engine of 3C 273 where quasar. Fits of the VLBI data suggest a period of precession the rapid precession is tidally induced in the primary accretion of 16 years in the observer’s frame. For a Hubble constant ∼ −1 −1 disk inner region by a secondary black hole in a non-coplanar parameter h =0.7 (H0 = 100h km s Mpc ), the jet would orbit. Using γ- and X-ray data we estimate upper limits for the have a bulk Lorentz factor γ 10.8 and precess within a cone mass of the primary, and then we compute the relevant parame- of half-opening angle 3.9◦∼. The Doppler factor should vary ters of the system for a variety of disk models. We also discuss between 2.8 and 9.4 due∼ to the changing viewing angle. The some of the implications of the model for the electromagnetic implications of such an oscillation in the value of the Doppler and gravitational radiation from 3C 273. factor for the observable emission along the electromagnetic spectrum of 3C 273 were explored in Paper I. Key words: galaxies: quasars: individual: 3C 273 – gamma In this paper we present and discuss a supermassive bi- rays: theory – black hole physics nary black hole model which could explain the jet precession in 3C 273. We shall assume that the inner jet and the innermost parts of the accretion disk that surrounds the primary black hole are coupled in such a way that a precession of the disk induces a 1. Introduction precession of the jet, as it is thought to occur in galactic binary The bright radio source 3C 273 is one of the most extensively systems like SS433 (e.g. Katz 1980). A secondary black hole studied active galactic nucleus. It was first identified as a quasar in a close non-coplanar orbit can exert a tidal perturbation on at redshift z =0.158 by Schmidt (1963). Detailed observations the disk that can result in the near-rigid body precession of its of this object have been performed during more than 35 years, innermost regions (e.g. Katz 1997). We shall use γ- and X-ray including simultaneous measurements of its spectrum from ra- data, along with the information obtained from the VLBI ra- dio to γ-ray energies (Lichti et al. 1995) and multiwavelengths dio observations, to constrain the black hole masses and other variability studies for equally wide energy ranges (von Mon- parameters of the system. tigny et al. 1997). Supermassive black hole binaries (SBHBs) are the natural 3C 273 has been also subject to intense VLBI monitoring result of galaxy mergers. Their formation and evolution have since Cohen et al. (1971) measured its superluminal expansion been extensively discussed in the literature (e.g. Begelman et velocity. At least ten superluminal components have been de- al. 1980, Roos 1981, Valtaoja et al. 1989). The fact that many tected moving away from the optically thick radio core (e.g. Un- (if not most) galaxies contain massive black holes and that galax- win et al. 1985, Biretta et al. 1985, Cohen et al. 1987; Zensus et ies often merge implies a relatively high formation rate of SB- al. 1988, 1990; Krichbaum et al. 1990, Abraham et al. 1996). Ad- HBs. The current evidence for central engines of active galactic ditional short-lived components have been almost surely missed nuclei formed by massive binary systems includes double nu- during the gaps between observations. clei (as in the case of NGC4486B), wiggly jets (e.g. Kaastra & Roos 1992), double emission lines observed in several quasars Send offprint requests to: G.E. Romero ([email protected]) (Gaskell 1996), and periodic optical light curves as in the case ? Membern of CONICET 58 G.E. Romero et al.: Beaming and precession in the inner jet of 3C 273. II of OJ 287 (Sillanpa¨a¨ et al. 1988, Lehto & Valtonen 1996, Villata et al. 1998). Geodetic precession of relativistic jets in SBHBs has also been often discussed in relation to large-scale helical jets (e.g. Begelman et al. 1980, Roos 1988). This effect is due to the Lense-Thirring dragging of inertial frames and is much slower than the tidal induced precession that will be studied here. The geodetic precession of the primary in SBHBs occurs with a 8 5/2 −3/2 period of Pgeod 9 10 r (M/m)M yr, where r is ∼ × 8 the black hole separation in pc, M8 the mass of the primary in units of 108 M , and M/m is the primary to secondary mass ratio. This kind of precession cannot be applied to stable sources with short periods ( a few years) because gravitational losses rapidly become catastrophic.∼ Roos et al. (1993) have studied the small-scale wiggling jet of 1928+738 in the context of a binary black hole system, using Fig. 1. A sketch (drawn not at scale) of the precessing disk model for a different approach: they have assumed that the jet complex 3C 273. Jet direction is indicated by ωd. structure is the result of the velocity modulation produced by the orbital motion of the hole that accelerates the jet in the supermassive binary. wood 1997, 1998; Terquem et al. 1999; Wijers & Pringle 1999). In the case of 3C 273, where the existence of a prominent ac- However, except by the paper by Katz (1997) on OJ 287, the ap- plication of tidally-driven precession to blazars remains mostly cretion disk around the primary can be inferred form the strong 1 blue bump in the spectrum (e.g. Malkan 1983, Kriss et al. 1999), unexplored. a tidally induced precession of the jet seems to be the more plau- sible explanation of the jet behaviour at VLBI scales. In the next 2.2. Dynamics sections we will discuss the details of this scenario. The dynamics of the disk is determined by the equations of motion and continuity. They can be written as: 2. Disk tidal perturbation ∂v 1 +(v∇)v = ∇P ∇Φ+f visc (1) 2.1. Framework ∂t −ρ − Let us consider a central black hole of mass M surrounded by and an accretion disk with inner radius rin and outer radius rout. ∂ρ + ∇(ρv)=0, (2) Self-gravity is assumed to be negligible up to distances of ∂t few hundreds of r from the hole, where r = GM/c2 is the∼ g g where P denotes the pressure, ρ the density, v the velocity of gravitational radius (Sakimoto & Coroniti 1981). Two relativis- the fluid, f the viscous force per unit of mass, and Φ is the tic jets are collimated perpendicularly to the disk near the central visc external gravitational potential given by: black hole and propagate in opposite directions. A secondary hole of mass m is in a circular non-coplanar orbit of radius rm Φ=ΦM +Φm with an inclination angle θ to the plane of the disk. It is expected GM Gm Gm r.rm that the tidal interactions between the disk and the secondary = + 3 . (3) − r − r rm r result in the precession of the innermost part of the disk, where | − | m the communication among the different fluid elements can be The first term in the second member of Eq. (3) is the potential sufficiently fast to allow a near-rigid body behaviour. This disk due to the primary whereas the other two terms are the effect of precession is transmitted to the jets, which also precess at the the perturbing action of the secondary. same rate within a cone of half-opening angle θ. The equation of state is assumed to be polytropic: A sketch of the situation is presented in Fig. 1, where the or- P = Kρ1+1/n, (4) bital plane of the binary system is coincident with the xy-plane. Just one of the jets and the precessing part of the disk, whose where K and n are the polytropic constant and index, respec- outer radius is rd, are represented here. The disk Keplerian an- tively. The sound speed is 3 1/2 gular velocity is ωd =(GM/rd) .