STATIONARY SHEATH OF FARADAY ROTATION IN THE JET OF 3C 120

2010 ◽  
Vol 19 (06) ◽  
pp. 917-922
Author(s):  
JOSÉ L. GÓMEZ ◽  
MAR ROCA-SOGORB ◽  
IVÁN AGUDO ◽  
ALAN P. MARSCHER ◽  
SVETLANA G. JORSTAD
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Radio Galaxy ◽  
External Medium ◽  
Degree Of Polarization ◽  
Polarization Structure ◽  
Rotation Measure ◽  
Helical Magnetic Field ◽  
3C 120 ◽  
Two Fluid

We present a sequence of 12 monthly polarimetric multi-frequency VLBA observations of the radio galaxy 3C 120. The motion of multiple superluminal components allows the mapping of the polarization structure along most of the jet and across its width, revealing a coherent in time Faraday screen and RM-corrected polarization angles. Gradients in Faraday rotation and degree of polarization across the jet are observed, together with a localized region of high rotation measure superposed on this structure. This is explained as produced by the presence of a helical magnetic field in a two-fluid jet model, consisting of an inner emitting jet and a sheath containing nonrelativistic electrons. Interaction of the jet with the external medium would explain the confined region of enhanced Faraday rotation.

scholarly journals Faraday Rotation and Polarization Gradients in the Jet of 3C 120: Interaction with the External Medium and a Helical Magnetic Field?

2008 ◽  
Vol 681 (2) ◽  
pp. L69-L72 ◽  
Author(s):  
José L. Gómez ◽  
Alan P. Marscher ◽  
Svetlana G. Jorstad ◽  
Iván Agudo ◽  
Mar Roca-Sogorb
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
External Medium ◽  
Helical Magnetic Field ◽  
3C 120

Probing the B-fields of AGN jets on kiloparsec scales - NGC 6251

2018 ◽  
Vol 14 (S342) ◽  
pp. 244-245
Author(s):  
Sebastian Knuettel ◽  
Denise Gabuzda
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Large Scale ◽  
Outward Current ◽  
Electrical Current ◽  
Line Of Sight ◽  
Astrophysical Jets ◽  
Rotation Measure ◽  
Jet Structure ◽  
Helical Magnetic Field

AbstractBy constructing images of the Faraday rotation measure (RM) of large scale astrophysical jets, the line-of-sight magnetic field component and electron density in the region of Farady rotation can be investigated. A significant gradient in the RM transverse to the jet direction may indicate a corresponding gradient in the line-of-sight magnetic field, implying a toroidal or helical magnetic field, which would, in turn, imply the presence of an associated electrical current in the jet. The detection of such large scale gradients can reliably demonstrate that helical or toroidal fields can persist to large distances from the central AGN. We present a kiloparsec-scale Faraday rotation map of NGC 6251 that shows statistically significant transverse RM gradients across its kiloparsec scale jet structure that imply an outward current.

scholarly journals HELICAL MAGNETIC FIELDS IN RELATIVISTIC JETS THROUGH FARADAY ROTATION AND JET STRATIFICATION STUDIES

2012 ◽  
Vol 08 ◽  
pp. 265-270
Author(s):  
JOSÉ L. GÓMEZ ◽  
CAROLINA CASADIO ◽  
MAR ROCA-SOGORB ◽  
IVÁN AGUDO ◽  
ALAN P. MARSCHER ◽  
...  
Keyword(s):  
Magnetic Fields ◽  
Faraday Rotation ◽  
Galactic Nuclei ◽  
Relativistic Jets ◽  
Long Baseline ◽  
Rotation Measure ◽  
Very Long Baseline Array ◽  
Helical Magnetic Field ◽  
3C 120 ◽  
Emission Stratification

Helical magnetic fields may play an important role in the formation, collimation, and acceleration of relativistic jets in active galactic nuclei. These may be searched for by looking for Faraday rotation measure (RM) gradients and emission stratification across the jet width. Multi-epoch polarimetric Very Long Baseline Array (VLBA) observations of the radio galaxy 3C 120 have revealed the existence of such a RM gradient across the jet, but the presence of a localized region of enhanced RM and uncorrelated changes in the polarization of the underlying jet emission and the Faraday rotation screen suggest that a significant fraction of the RM found in 3C 120 originates in foreground clouds. Thanks to the combination of 48 images spanning 14 years of 15 GHz VLBA observations of 3C 273 we have found a stratification in total intensity across the jet that flips sides with distance along the jet, supporting a model in which the jet of 3C 273 accelerates and is threaded by a helical magnetic field.

scholarly journals PARSEC-SCALE INVESTIGATION OF THE MAGNETIC FIELD STRUCTURE OF SEVERAL AGN JETS

2008 ◽  
Vol 17 (09) ◽  
pp. 1553-1560 ◽  
Author(s):  
S. P. O'SULLIVAN ◽  
D. C. GABUZDA
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Reliable Determination ◽  
Long Baseline ◽  
Central Engine ◽  
Relativistic Jet ◽  
Rotation Measure ◽  
Transverse Rotation ◽  
Helical Magnetic Field ◽  
The Magnetic Field

Multi-frequency (4.6, 5, 5.5, 8, 8.8, 13, 15, 22 & 43 GHz) polarization observations of six "blazars" were obtained on the American Very Long Baseline Array (VLBA) over a 24-hr period on 2 July 2006. Observing at several frequencies, separated by short and long intervals, enabled reliable determination of the distribution of Faraday rotation on a range of scales. In all cases the magnitude of the RM increases in the higher frequency observations, implying that the electron density and/or magnetic field strength is increasing as we get closer to the central engine. After correcting for Faraday rotation, the polarization orientation in the jet is either parallel or perpendicular to the jet direction. A transverse rotation measure (RM) gradient was detected in the jet of 0954+658, providing evidence for the presence of a helical magnetic field surrounding the jet. For three of the sources (0954+658, 1418+546, 2200+420), the sign of the RM in the core region changes in different frequency-intervals, indicating that the line-of-sight component of the magnetic field is changing with distance from the base of the jet. We suggest an explanation for this in terms of bends in a relativistic jet surrounded by a helical magnetic field; where there is no clear evidence for pc-scale bends, the same effect can be explained by an accelerating/decelerating jet.

scholarly journals Magnetized filament models for diverging plasma lenses

2020 ◽  
Vol 493 (2) ◽  
pp. 1736-1752
Author(s):  
Adam Rogers ◽  
Abdul Mohamed ◽  
Bailey Preston ◽  
Jason D Fiege ◽  
Xinzhong Er
Keyword(s):  
Magnetic Field ◽  
Column Density ◽  
Volume Density ◽  
Magnetized Plasma ◽  
Gravitational Lens ◽  
Line Of Sight ◽  
Density Distributions ◽  
Rotation Measure ◽  
Spherical Plasma ◽  
Helical Magnetic Field

ABSTRACT Spherical plasma lens models are known to suffer from a severe overpressure problem, with some observations requiring lenses with central pressures up to millions of times in excess of the ambient interstellar medium. There are two ways that lens models can solve the overpressure problem: a confinement mechanism exists to counter the internal pressure of the lens, or the lens has a unique geometry, such that the projected column-density appears large to an observer. This occurs with highly asymmetric models, such as edge-on sheets or filaments, with potentially low volume–density. In the first part of this work we investigate the ability of non-magnetized plasma filaments to mimic the magnification of sources seen behind spherical lenses and we extend a theorem from gravitational lens studies regarding this model degeneracy. We find that for plasma lenses, the theorem produces unphysical charge density distributions. In the second part of the work, we consider the plasma lens overpressure problem. Using magnetohydrodynamics, we develop a non self-gravitating model filament confined by a helical magnetic field. We use toy models in the force-free limit to illustrate novel lensing properties. Generally, magnetized filaments may act as lenses in any orientation with respect to the observer, with the most high-density events produced from filaments with axes near the line of sight. We focus on filaments that are perpendicular to the line of sight that show the toroidal magnetic field component may be observed via the lens rotation measure.

scholarly journals ON THE SOURCE OF FARADAY ROTATION IN THE JET OF THE RADIO GALAXY 3C 120

2011 ◽  
Vol 733 (1) ◽  
pp. 11 ◽  
Author(s):  
José L. Gómez ◽  
Mar Roca-Sogorb ◽  
Iván Agudo ◽  
Alan P. Marscher ◽  
Svetlana G. Jorstad
Keyword(s):  
Faraday Rotation ◽  
Radio Galaxy ◽  
3C 120

scholarly journals Fluctuation dynamos and their Faraday rotation signatures

2012 ◽  
Vol 10 (H16) ◽  
pp. 400-400
Author(s):  
Pallavi Bhat ◽  
Kandaswamy Subramanian
Keyword(s):  
Magnetic Field ◽  
Simple Model ◽  
Faraday Rotation ◽  
High Field ◽  
Line Of Sight ◽  
Simulation Data ◽  
Thermal Electron ◽  
Volume Filling ◽  
Rotation Measure ◽  
The Magnetic Field

We study fluctuation dynamo (FD) action in turbulent systems like galaxy-clusters focusing on the Faraday rotation signature. This is defined as RM = K ∫LneB ⋅ dl where ne is the thermal electron density, B is the magnetic field, the integration is along the line of sight from the source to the observer, and K = 0.81 rad m−2 cm−3 μG−1 pc−1. We directly compute, using the simulation data, ∫ B ⋅ dl, and hence the Faraday rotation measure (RM) over 3N2 lines of sight, along each x, y and z-directions. We normalise the RM by the rms value expected in a simple model, where a field of strength Brms fills each turbulent cell but is randomly oriented from one turbulent cell to another. This normalised RM is expected to have a nearly zero mean but a non-zero dispersion, σRM. We show in Fig. 1a and 1b, that a suite of simulations, on saturation, obtain the value of σRM = 0.4−0.5, and this is independent of PM, RM and the resolution of the run. This is a fairly large value for an intermittent random field; as it is of order 40%–50%, of that expected in a model where Brms strength fields volume fill each turbulent cell, but are randomly oriented from one cell to another. We also find that the regions with a field strength larger than 2Brms contribute only 15–20% to the total RM (see Fig. 1a). This shows that it is the general ‘sea’ of volume filling fluctuating fields that contribute dominantly to the RM produced, rather than the the high field regions.

scholarly journals The jets of AGN as giant coaxial cables

2018 ◽  
Vol 612 ◽  
pp. A67 ◽  
Author(s):  
Denise C. Gabuzda ◽  
Matt Nagle ◽  
Naomi Roche
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Faraday Rotation ◽  
Toroidal Magnetic Field ◽  
Systematic Change ◽  
Physical Mechanisms ◽  
Preferred Direction ◽  
Long Baseline ◽  
Rotation Measure ◽  
Very Long Baseline Array

Context. The currents carried by the jets of active galactic nuclei (AGNs) can be probed using maps of the Faraday rotation measure (RM), since a jet current will be accompanied by a toroidal magnetic field, which will give rise to a systematic change in the RM across the jet. Aims. The aim of this study is to identify new AGNs displaying statistically significant transverse RM gradients across their parsec-scale jets, in order to determine how often helical magnetic fields occur in AGN jets, and to look for overall patterns in the implied directions for the toroidal field components and jet currents. Methods. We have carried out new analyses of Faraday RM maps derived from previously published 8.1, 8.4, 12.1 and 15.3 GHz data obtained in 2006 on the NRAO Very Long Baseline Array (VLBA). In a number of key ways, our procedures were identical to those of the original authors, but the new imaging and analysis differs from the original methods in several ways: the technique used to match the resolutions at the different frequencies, limits on the widths spanned by the RM gradients analyzed, treatment of core-region RM gradients, approach to estimation of the significances of the gradients analyzed, and inclusion of a supplementary analysis using circular beams with areas equal to those of the corresponding elliptical naturally weighted beams. Results. This new analysis has substantially increased the number of AGNs known to display transverse RM gradients that may reflect the presence of a toroidal magnetic-field component. The collected data on parsec and kiloparsec scales indicate that the current typically flows inward along the jet axis and outward in a more extended region surrounding the jet, typical to the current structure of a co-axial cable, accompanied by a self-consistent system of nested helical magnetic fields, whose toroidal components give rise to the observed transverse Faraday rotation gradients. Conclusions. The new results presented here make it possible for the first time to conclusively demonstrate the existence of a preferred direction for the toroidal magnetic-field components – and therefore of the currents – of AGN jets. Discerning the origin of this current-field system is of cardinal importance for understanding the physical mechanisms leading to the formation of the intrinsic jet magnetic field, which likely plays an important role in the propagation and collimation of the jets; one possibility is the action of a “cosmic battery”.

scholarly journals AGN dusty plasma polarization features

2014 ◽  
Vol 10 (S313) ◽  
pp. 352-357
Author(s):  
Ericson D. Lopez ◽  
Susana Deustua
Keyword(s):  
Magnetic Field ◽  
Electromagnetic Radiation ◽  
Faraday Rotation ◽  
Significant Contribution ◽  
Theoretical Study ◽  
Outer Region ◽  
Dust Particles ◽  
Rotation Measure ◽  
Electrons And Ions ◽  
The Magnetic Field

AbstractWe present the results of a theoretical study on the influence of dust particles on the polarization properties of the radiation that propagates along the jet in AGNs. First, a model for describing the interaction of dust particles, in addition to the electrons and ions, with electromagnetic radiation in a magneto-active plasma has been developed. From here, the contribution of dust particles to the Faraday rotation of the plane of polarization of the electric vector can be deduced. This model is evaluated for the outer region of the jet where the presence of dust particles are assumed, the magnetic field is weak and the electron density is low. Our results show that the dust particles give a significant contribution to the linear Faraday rotation measure.

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