Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei. II. Prediction from Our Sweeping Magnetic Twist Model for the Wiggled Parts of Active Galactic Nucleus Jets and Tails

Kigure, Hiromitsu; Uchida, Yutaka; Nakamura, Toshikazu; Hirose, Shigenobu; Cameron, R. H.

doi:10.1086/386538

Cited by 13 publications

(10 citation statements)

References 35 publications

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“…5a and 6a of Uchida et al 2004). In addition, rotation measure gradients perpendicular to the jet axis (Asada et al 2002;Gabuzda et al 2004;Zavala & Taylor 2005) and a distribution of the rotation measure associated with the jet deformation (Feretti et al 1999) are reproduced numerically by the MHD model Kigure et al 2004). These points show the advantages of the MHD model.…”

Section: Introductionmentioning

confidence: 92%

Three‐dimensional Magnetohydrodynamic Simulations of Jets from Accretion Disks

Kigure

Shibata

2005

ApJ

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We report the results of three-dimensional magnetohydrodynamic ( MHD) simulations of a jet formation by the interaction between an accretion disk and a large-scale magnetic field. The disk is not treated as a boundary condition but is solved self-consistently. To investigate the stability of the MHD jet, the accretion disk is perturbed with a nonaxisymmetric sinusoidal or random fluctuation of the rotational velocity. The dependences of the jet velocity (v z ), mass outflow rate (Ṁ w ), and mass accretion rate (Ṁ a ) on the initial magnetic field strength in both nonaxisymmetric cases are similar to those in the axisymmetric case. That is, v z / B 1 = 3 0 ,Ṁ w / B 0 , anḋ M a / B 1:4 0 , where B 0 is the initial magnetic field strength. The former two relations are consistent with Michel's steady solution, v z / (B 2 0 /Ṁ w ) 1 = 3 , although the jet and accretion do not reach the steady state. In both perturbation cases, a nonaxisymmetric structure with m ¼ 2 appears in the jet, where m is the azimuthal wavenumber. This structure cannot be explained by Kelvin-Helmholtz instability and seems to originate in the accretion disk. Nonaxisymmetric modes in the jet reach almost constant levels after about 1.5 orbital periods of the accretion disk, while all modes in the accretion disk grow with oscillation. As for the angular momentum transport by Maxwell stress, the vertical component, hB B z /4 i, is comparable to the radial component, hB B r /4 i, in the wide range of initial magnetic field strength.

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Section: Introductionmentioning

confidence: 92%

Three‐dimensional Magnetohydrodynamic Simulations of Jets from Accretion Disks

Kigure

Shibata

2005

ApJ

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“…A 90° change of the EVPA can be initiated by already a small deviation of the jet direction caused, for example, by the precession of the jet base (if θ∼ 1/Γ, in order to change the observed EVPA by an angle of the order of unity, the real direction may change by Δθ≪ 1/Γ). Similarly, a slight acceleration of the jet or injection of a small amount of the additional toroidal magnetic flux (as in the ‘sweeping magnetic twist’ model of Nakamura, Uchida & Hirose 2001 and Kigure et al 2004). On the other hand, a relativistic jet viewed at a large angle, θ≫ 1/Γ, will be either weakly polarized along the jet (for B ′ φ ≥ B ′ z ) or strongly polarized orthogonally to the jet (for B ′ φ ≤ B ′ z ); see Fig.…”

Section: Hollow Cylindrical Jetsmentioning

confidence: 99%

Polarization and structure of relativistic parsec-scale AGN jets

Lyutikov

Pariev

Gabuzda

2005

Monthly Notices of the Royal Astronomical Society

250

308

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We consider the polarization properties of optically thin synchrotron radiation emitted by relativistically moving electron-positron jets carrying large-scale helical magnetic fields. In our model, the jet is cylindrical and the emitting plasma moves parallel to the jet axis with a characteristic Lorentz factor Gamma. We draw attention to the strong influence that the bulk relativistic motion of the emitting relativistic particles has on the observed polarization. Our computations predict and explain the following behaviour. (i) For jets unresolved in the direction perpendicular to their direction of propagation, the position angle of the electric vector of the linear polarization has a bimodal distribution, being oriented either parallel or perpendicular to the jet. (ii) If an ultra-relativistic jet with Gamma >> 1 whose axis makes a small angle to the line of sight, theta similar to 1/Gamma, experiences a relatively small change in the direction of propagation, velocity or pitch angle of the magnetic fields, the polarization is likely to remain parallel or perpendicular; on the other hand, in some cases, the degree of polarization can exhibit large variations and the polarization position angle can experience abrupt 90 degrees. changes. This change is more likely to occur in jets with flatter spectra. (iii) In order for the jet polarization to be oriented along the jet axis, the intrinsic toroidal magnetic field ( in the frame of the jet) should be of the order of or stronger than the intrinsic poloidal field; in this case, the highly relativistic motion of the jet implies that, in the observer's frame, the jet is strongly dominated by the toroidal magnetic field B(phi)/B(z) >= Gamma. (iv) The emission-weighted average pitch angle of the intrinsic helical field in the jet must not be too small to produce polarization along the jet axis. In force-free jets with a smooth distribution of emissivities, the emission should be generated in a limited range of radii not too close to the jet core. ( v) For mildly relativistic jets, when a counter-jet can be seen, the polarization of the counter-jet is preferentially orthogonal to the axis, unless the jet is strongly dominated by the toroidal magnetic field in its rest frame. ( vi) For resolved jets, the polarization pattern is not symmetric with respect to jet axis. Under certain conditions, this can be used to deduce the direction of the spin of the central object ( black hole or disc), whether it is aligned or anti-aligned with the jet axis. (vii) In resolved 'cylindrical shell' type jets, the central parts of the jet are polarized along the axis, while the outer parts are polarized orthogonal to it, in accordance with observations. We conclude that large-scale magnetic fields can explain the salient polarization properties of parsec-scale AGN jets. Since the typical degrees of polarization are <= 15 per cent, the emitting parts of the jets must have comparable rest-frame toroidal and poloidal fields. In this case, most relativistic jets are strongly dominated by the ...

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“…Similarly, a slight acceleration of the jet or injection of a small amount of the additional toroidal magnetic flux (as in the 'sweeping magnetic twist' model of Nakamura, Uchida &Hirose 2001 andKigure et al 2004). On the other hand, a relativistic jet viewed at a large angle, θ 1/ , will be either weakly polarized along the jet (for B φ B z ) or strongly polarized orthogonally to the jet (for B φ B z ); see Fig.…”

Section: Unresolved Hollow Jets (Cylindrical Shell)mentioning

confidence: 99%

Polarization and Structure of Relativistic Parsec-Scale AGN Jets

Lyutikov¹

2004

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Author(s)Lyutikov, M.; Pariev, V. I.; Gabuzda, Denise Publication date 2005Original citation Lyutikov, M., Pariev, V. I. and Gabuzda, D. C. (2005) ABSTRACTWe consider the polarization properties of optically thin synchrotron radiation emitted by relativistically moving electron-positron jets carrying large-scale helical magnetic fields. In our model, the jet is cylindrical and the emitting plasma moves parallel to the jet axis with a characteristic Lorentz factor . We draw attention to the strong influence that the bulk relativistic motion of the emitting relativistic particles has on the observed polarization. Our computations predict and explain the following behaviour. (i) For jets unresolved in the direction perpendicular to their direction of propagation, the position angle of the electric vector of the linear polarization has a bimodal distribution, being oriented either parallel or perpendicular to the jet. (ii) If an ultra-relativistic jet with 1 whose axis makes a small angle to the line of sight, θ ∼ 1/ , experiences a relatively small change in the direction of propagation, velocity or pitch angle of the magnetic fields, the polarization is likely to remain parallel or perpendicular; on the other hand, in some cases, the degree of polarization can exhibit large variations and the polarization position angle can experience abrupt 90• changes. This change is more likely to occur in jets with flatter spectra. (iii) In order for the jet polarization to be oriented along the jet axis, the intrinsic toroidal magnetic field (in the frame of the jet) should be of the order of or stronger than the intrinsic poloidal field; in this case, the highly relativistic motion of the jet implies that, in the observer's frame, the jet is strongly dominated by the toroidal magnetic field B φ /B z . (iv) The emission-weighted average pitch angle of the intrinsic helical field in the jet must not be too small to produce polarization along the jet axis. In force-free jets with a smooth distribution of emissivities, the emission should be generated in a limited range of radii not too close to the jet core. (v) For mildly relativistic jets, when a counter-jet can be seen, the polarization of the counter-jet is preferentially orthogonal to the axis, unless the jet is strongly dominated by the toroidal magnetic field in its rest frame. (vi) For resolved jets, the polarization pattern is not symmetric with respect to jet axis. Under certain conditions, this can be used to deduce the direction of the spin of the central object (black hole or disc), whether it is aligned or anti-aligned with the jet axis. (vii) In resolved 'cylindrical shell' type jets, the central parts of the jet are polarized along the axis, while the outer parts are polarized orthogonal to it, in accordance with observations.We conclude that large-scale magnetic fields can explain the salient polarization properties of parsec-scale AGN jets. Since the typical degrees of polarization are 15 per cent, the emitting parts of the jets must have comparable rest-fram...

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Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei. II. Prediction from Our Sweeping Magnetic Twist Model for the Wiggled Parts of Active Galactic Nucleus Jets and Tails

Cited by 13 publications

References 35 publications

Three‐dimensional Magnetohydrodynamic Simulations of Jets from Accretion Disks

Three‐dimensional Magnetohydrodynamic Simulations of Jets from Accretion Disks

Polarization and structure of relativistic parsec-scale AGN jets

Polarization and Structure of Relativistic Parsec-Scale AGN Jets

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