Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec‐Scale Accelerations

Vlahakis, N.; Königl, Arieh

doi:10.1086/382670

Cited by 224 publications

(257 citation statements)

References 34 publications

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“…In Model 3, a higher value of µ was required, and the resulting conversion from Poynting flux to kinetic energy is slower. In all three cases, the Alfvénic point is found to be located close to the light cylinder, in agreement with exact self-similar solutions (Vlahakis & Königl 2004). The fast magnetosonic point is located at r ∼ 0.4 mas, corresponding to z ∼ 1 mas, and in agreement with the expectation that γ FMP µ 1/3 .…”

Section: Wind Solutionssupporting

confidence: 87%

“…Since this deviation is small, the fluid is only slowly accelerated by a small residual force and the acceleration zone can extend over a large distance. Both numerical simulations and observational evidence suggest that jet acceleration continues up to distances of 10 4 -10 5 R s from the central engine (Vlahakis & Königl 2004;Lobanov & Zensus 1996Homan et al 2015;Lee et al 2008Lee et al , 2016.…”

Section: Jet Collimation and Accelerationmentioning

confidence: 97%

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Kinematics of the jet in M 87 on scales of 100–1000 Schwarzschild radii

Mertens

Lobanov

Walker

et al. 2016

A&A

221

266

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Context. Very long baseline interferometry (VLBI) imaging of radio emission from extragalactic jets provides a unique probe of physical mechanisms governing the launching, acceleration, and collimation of relativistic outflows. Aims. VLBI imaging of the jet in the nearby active galaxy M 87 enables morphological and kinematic studies to be done on linear scales down to ∼ 100 Schwarzschild radii (R s ). Methods. The two-dimensional structure and kinematics of the jet in M 87 (NGC 4486) have been studied by applying the Waveletbased Image Segmentation and Evaluation (WISE) method to 11 images obtained from multi-epoch Very Long Baseline Array (VLBA) observations made in January-August 2007 at 43 GHz (λ = 7 mm).Results. The WISE analysis recovers a detailed two-dimensional velocity field in the jet in M 87 at sub-parsec scales. The observed evolution of the flow velocity with distance from the jet base can be explained in the framework of MHD jet acceleration and Poynting flux conversion. A linear acceleration regime is observed up to z obs ∼ 2 mas. The acceleration is reduced at larger scales, which is consistent with saturation of Poynting flux conversion. Stacked cross correlation analysis of the images reveals a pronounced stratification of the flow. The flow consists of a slow, mildly relativistic layer (moving at β ∼ 0.5 c), associated either with instability pattern speed or an outer wind, and a fast, accelerating stream line (with β ∼ 0.92, corresponding to a bulk Lorentz factor γ ∼ 2.5). A systematic difference of the apparent speeds in the northern and southern limbs of the jet is detected, providing evidence for jet rotation. The angular velocity of the magnetic field line associated with this rotation suggests that the jet in M87 is launched in the inner part of the disk, at a distance r 0 ∼ 5 R s from the central engine.Conclusions. The combined results of the analysis imply that MHD acceleration and conversion of Poynting flux to kinetic energy play the dominant roles in collimation and acceleration of the flow in M 87.

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Section: Wind Solutionssupporting

confidence: 87%

Section: Jet Collimation and Accelerationmentioning

confidence: 97%

Kinematics of the jet in M 87 on scales of 100–1000 Schwarzschild radii

Mertens

Lobanov

Walker

et al. 2016

A&A

221

266

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“…They concluded that the observed acceleration is not likely to be a geometrical effect, but should reflect the physical acceleration of plasma. The possibility of the intrinsic acceleration of jet features on parsec scales was discussed by Vlahakis & Königl (2004). There it was specifically argued that the acceleration observed in 3C 345 is not purely hydrodynamic, but can be attributed to magnetic driving.…”

Section: Discussionmentioning

confidence: 99%

Relativistic outflow drivesγ-ray emission in 3C 345

Schinzel

Lobanov

Taylor

et al. 2012

A&A

100

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Aims. On the basis of the first 20 months of Fermi-LAT data and optical monitoring, the quasar 3C 345 has been identified as a γ-ray emitter. We investigate whether there is a connection between the γ-ray and optical variability of 3C 345 and the properties of its parsec-scale radio emission. Methods. We combined the Fermi-LAT data of 3C 345, covering an energy range of 0.1-300 GeV, with 32 Very Long Baseline Array observations of the object made at 43.2 GHz in the period of January 2008-March 2010.Results. The VLBA data reveal the morphology and kinematics of the flow on scales of up to ≈5 milliarcseconds (deprojected linear distances of 380 parsecs). The brightness temperature, T b (r), measured along the jet first decreases with distance ∝r −(0.95 ± 0.69) and later exhibits a break at ≈0.3 milliarcseconds (mas), with T b (r) ∝ r −(4.11 ± 0.85) at larger separations. Variations in the γ-ray, optical, and parsec-scale radio emission display a similar long-term trend that persists during the entire VLBA monitoring period. The γ-ray and optical variations on shorter timescales are related to structural changes in the jet on scales of ≈0.3 mas (≈23 parsecs, deprojected), with the γ-ray and optical flares possibly being related to the evolution of four distinct superluminal components identified in the flow. Conclusions. The observations indicate that both the quiescent and flaring components of the γ-ray emission are produced in a region of the jet that extends up to ∼23 pc. This region may correspond to the Compton-loss dominated zone of the flow and its large extent may favor the synchrotron self-Compton mechanism for γ-ray production in the relativistic jet of the quasar 3C 345.

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“…Some numerical simulations (McKinney & Gammie 2004;De Villiers et al 2005) have suggested that launching from the accretion disk can only produce jets with moderate Lorentz factors (Γ < 3), while a process involving the black hole rotation can achieve Γ ∼ 10 more easily (McKinney 2006). However, it is not ruled out that the inner disk can launch relativistic jets as well (Vlahakis & Königl 2004;Komissarov et al 2007). The possibility of reaching a certain terminal Lorentz factor depends strictly on the details of the process which converts the initially magnetically dominated jet into a kinetically dominated one.…”

Section: Introductionmentioning

confidence: 99%

The stratified two-sided jet of Cygnus A

Boccardi

Krichbaum

Bach

et al. 2015

A&A

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Aims. High-resolution Very-Long-Baseline Interferometry (VLBI) observations of relativistic jets are essential for constraining the fundamental parameters of jet formation models. At a distance of 249 Mpc, Cygnus A is a unique target for such studies, since it is the only Fanaroff-Riley Class II radio galaxy for which a detailed subparsec scale imaging of the base of both jet and counter-jet can be obtained. Observing at millimeter wavelengths unveils those regions that appear self-absorbed at longer wavelengths and enables an extremely sharp view toward the nucleus to be obtained. Methods. We performed 7 mm Global VLBI observations, achieving ultra-high resolution imaging on scales down to 90 µas. This resolution corresponds to a linear scale of only ∼400 Schwarzschild radii (for M BH = 2.5 × 10 9 M ). We studied the kinematic properties of the main emission features of the two-sided flow and probed its transverse structure through a pixel-based analysis. Results. We suggest that a fast and a slow layer with different acceleration gradients exist in the flow. The extension of the acceleration region is large (∼10 4 R S ), indicating that the jet is magnetically driven. The limb brightening of both jet and counter-jet and their large opening angles (φ J ∼ 10 • ) strongly favour a spine-sheath structure. In the acceleration zone, the flow has a parabolic shape (r ∝ z 0.55 ± 0.07 ). The acceleration gradients and the collimation profile are consistent with the expectations for a jet in "equilibrium", achieved in the presence of a mild gradient of the external pressure (p ∝ z −k , k ≤ 2).

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Magnetic Driving of Relativistic Outflows in Active Galactic Nuclei. I. Interpretation of Parsec‐Scale Accelerations

Cited by 224 publications

References 34 publications

Kinematics of the jet in M 87 on scales of 100–1000 Schwarzschild radii

Kinematics of the jet in M 87 on scales of 100–1000 Schwarzschild radii

Relativistic outflow drivesγ-ray emission in 3C 345

The stratified two-sided jet of Cygnus A

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