Two-flow model for extragalactic radio jets

Sol, H.; Pelletier, G.; Asséo, E.

doi:10.1093/mnras/237.2.411

Cited by 199 publications

(144 citation statements)

References 4 publications

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“…ferent ways. It may reflect a 'two-fluid' jet (Sol et al 1989) comprising a relativistic beam (or spine) originating either from the magnetosphere of the central engine, or from the inner part of the accretion disk, and a non-relativistic wind originating from outer parts of the accretion disk (Tsinganos & Bogovalov 2002). The viability of this scenario has been tested in RMHD simulations of AGN jets (e.g.…”

Section: Jet Internal Structurementioning

confidence: 99%

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

Mertens

Lobanov

Walker

et al. 2016

A&A

235

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: Jet Internal Structurementioning

confidence: 99%

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

Mertens

Lobanov

Walker

et al. 2016

A&A

235

266

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“…We describe the ejection of a VLBI component in the framework of the two-fluid model (Sol et al 1989;Pelletier & Roland 1989, 1990Pelletier & Sol 1992), so we assume that:…”

Section: Astrophysical Phenomena Involved In the Optical Flux Variatimentioning

confidence: 99%

Long-termRandV-band monitoring of some suitable targets for the link between ICRF and the futureGaiacelestial reference frame

Taris

Andrei

Roland

et al. 2016

A&A

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Context. The Gaia astrometric mission of the European Space Agency was launched on December 2013. It will provide a catalog of 500 000 quasars. Some of these targets will be chosen to build an optical reference system that will be linked to the International Celestial Reference Frame (ICRF). The astrometric coordinates of these sources will have roughly the same uncertainty at both optical and radio wavelengths, and it is then mandatory to observe a common set of targets to build the link. In the ICRF, some targets have been chosen because of their pointlikeness. They are quoted as defining sources, and they ensure very good uncertainty about their astrometric coordinates. At optical wavelengths, a comparable uncertainty could be achieved for targets that do not exhibit strong astrophysical phenomena, which is a potential source of photocenter flickering. A signature of these phenomena is a magnitude variation at optical wavelengths. Aims. The goal of this work is to present the time series of 14 targets suitable for the link between the ICRF and the future Gaia Celestial Reference Frame. The observations have been done systematically by robotic telescopes in France and Chile once every two nights since 2011 and in two filters. These time series are analyzed to search for periodic or quasi-periodic phenomena that must be taken into account when computing the uncertainty about the astrometric coordinates. Methods. Two independent methods were used in this work to analyze the time series. We used the CLEAN algorithm to compare the frequency obtained to those given by the Lomb-Scargle method. It avoids misinterpreting the frequency peaks given in the periodograms. Results. For the 14 targets we determine some periods with a confidence level above 90% in each case. Some of the periods found in this work were not previously known. For the others, we did a comparative study of the periods previously studied by others and always confirm their values. All the periods given by the two methods are in good agreement with the difference always below 7.9% in the worst case. Finally we also present the structure functions for our two sets of objects (BL Lac and Seyfert galaxies). Conclusions. For all but one target, we find variations that could be the signature of periodic or quasi-periodic phenomena. Our time series could allow to bring some constraints on astrophysical models that could explain such variations. Binary black hole system, instabilities in the jet or in the accretion disk, changes in the torus structure are some of these astrophysical phenomena. They must be kept in mind when evaluating the uncertainty about the astrometric position of the targets suitable for the link between reference systems in a conservative way.

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“…The collimation of a central relativistic outflow can be provided by a non-relativistic MHD wind/jet produced by an accretion disk. Such a double jet structure was originally proposed by Sol et al (1989), and was investigated further by , Gracia et al (2005), and Beskin & Nokhrina (2006). The quasar systems with such efficiently collimated jets can be rare indeed due to the difficulties in developing the required large-scale poloidal magnetic fields in the geometrically thin accretion disks.…”

Section: The Spin Paradigmmentioning

confidence: 94%

Radio-loudness of active galaxies and the black hole evolution

Sikora

Stawarz

Lasota

2008

New Astronomy Reviews

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Active galactic nuclei (AGNs) form two distinct sequences on the radio-loudness -Eddington-ratio plane. The 'upper' sequence contains radio selected AGNs, the 'lower' sequence is composed mainly of optically selected AGNs. The sequences mark the upper bounds for the radio-loudness of two distinct populations of AGNs, hosted respectively by elliptical and disk galaxies. Both sequences show the same dependence of the radio-loudness on the Eddington ratio (an increase with decreasing Eddington ratio), which suggests that another parameter in addition to the accretion rate must play a role in determining the efficiency of jet production in AGNs. We speculate that this additional parameter is the spin of the black hole, assuming that black holes in giant elliptical galaxies have (on average) much larger spins than black holes in disc galaxies. Possible evolutionary scenarios leading to such a spin dichotomy are discussed. The galaxy-morphology related radio-dichotomy breaks down at high accretion rates where the dominant fraction of luminous quasars being hosted by giant ellipticals is radio quiet. This indicates that the production of powerful jets at high accretion rates is in most cases suppressed and, in analogy to X-ray binary systems (XRB) during high and very high states, may be intermittent. Such intermittency can be caused by switches between two different accretion modes, assuming that only during one of them an outflow from the central engine is sufficiently collimated to form a relativistic jet.

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Two-flow model for extragalactic radio jets

Cited by 199 publications

References 4 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

Long-termRandV-band monitoring of some suitable targets for the link between ICRF and the futureGaiacelestial reference frame

Radio-loudness of active galaxies and the black hole evolution

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