The Polarization of Cosmic Radio Waves

Gardner, F. F.; Whiteoak, J. B.

doi:10.1146/annurev.aa.04.090166.001333

Cited by 153 publications

(128 citation statements)

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“…Faraday rotation by a foreground screen can produce beam depolarization (Gardner & Whiteoak 1966). Longer wavelengths will exhibit this effect to a higher degree because of the k 2 nature of Faraday rotation.…”

Section: Fractional Polarization Propertiesmentioning

confidence: 99%

“…(12)- (13) RM gradient of 770 rad m À2 across a beam is sufficient to cause substantial depolarization at 8 GHz. To more quantitatively account for the observed fractional polarization, the beam depolarization can be modeled in the same manner as depolarization due to internal Faraday rotation (Gardner & Whiteoak 1966). The observed fractional polarization is a sinc function of the RM.…”

Section: Fractional Polarization Propertiesmentioning

confidence: 99%

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A View through Faraday’s Fog. II. Parsec‐Scale Rotation Measures in 40 Active Galactic Nuclei

Zavala

Taylor

2004

ApJ

109

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Section: Fractional Polarization Propertiesmentioning

confidence: 99%

Section: Fractional Polarization Propertiesmentioning

confidence: 99%

A View through Faraday’s Fog. II. Parsec‐Scale Rotation Measures in 40 Active Galactic Nuclei

Zavala

Taylor

2004

ApJ

109

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“…where p0 is the intrinsic fractional polarization and ǫ is the synchrotron emissivity at a depth along the line of sight (Burn 1966;Gardner & Whiteoak 1966;Sokoloff et al 1998). The polarization angle φ(x, y) is given by φ(x, y) = φ0 + 812…”

Section: Depolarization Toward the Radio Relicmentioning

confidence: 99%

JVLA S- and X-band polarimetry of the merging cluster Abell 2256

Ozawa

Nakanishi

Akahori

et al. 2015

Publications of the Astronomical Society of Japan

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We report polarimetry results of a merging cluster of galaxies Abell 2256 with Karl G. Jansky Very Large Array (JVLA). We performed new observations with JVLA at S-band (2051-3947 MHz) and X-band (8051-9947 MHz) in the C array configuration, and detected significant polarized emissions from the radio relic, Source A, and Source B in this cluster. We calculated the total magnetic field strengths toward the radio relic using revised equipartition formula, which is 1.8-5.0 µG. With dispersions of Faraday rotation measure, magnetic-field strengths toward Sources A and B are estimated to be 0.63-1.26 µG and 0.11-0.21 µG, respectively. An extremely high degree of linear polarization, as high as ∼ 35 %, about a half of the maximum polarization, was detected toward the radio relic, which indicates highly ordered magnetic lines of force over the beam sizes (∼ 52 kpc).The fractional polarization of the radio relic decreases from ∼ 35 % to ∼ 20 % around 3 GHz as the frequency decreases and is nearly constant between 1.37 and 3 GHz. Both analyses with depolarization models and Faraday tomography suggest multiple depolarization components toward the radio relic and imply the existence of turbulent magnetic fields.

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“…This phenomenon is known as the Faraday effect and the angle by which it rotates (Δψ) in a Faraday thin medium is proportional to the rotation measure (RM): Δψ = λ 2 RM. Furthermore, the RM is proportional to the line-of-sight integral over the density of thermal electrons multiplied by the strength of the regular field component parallel to the LOS: RM ∝ n e B dl (Gardner & Whiteoak 1966). With the RM distribution one can correct the polarization angles for Faraday rotation and also obtain information about the strength (if we have knowledge of n e ) and the direction of the Based on observations with the 100 m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg and the VLA operated by the NRAO.…”

Section: Introductionmentioning

confidence: 99%

Magnetic field structure and halo in NGC 4631

Mora

Krause

2013

A&A

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Context. All of the edge-on spiral galaxies observed so far present a similar magnetic field configuration, which consists of a planeparallel field in the disk and an X-shaped field at larger z-distances from the plane of the galaxy. Only NGC 4631 seems to have a different field orientation in its disk. Along the eastern and western halves of the disk of NGC 4631 the magnetic field orientation is parallel to the galactic plane, but in the central region of the disk a vertical field seems to dominate. Aims. In order to clarify whether NGC 4631 has a unique magnetic field configuration in the central region along its disk, we present high-resolution Faraday-corrected polarization data. Methods. Radio continuum observations of NGC 4631 at 4.85 GHz were performed with the VLA. In addition, observations were made with the Effelsberg telescope at 4.85 GHz and at 8.35 GHz. These were analyzed together with archival VLA-data at 8.35 GHz. The single-dish and interferometer data were combined to recover the missing zero-spacings. Results. We determined an integrated total spectral index of α tot = −0.78 ± 0.04 and a nonthermal integrated spectral index of α nth = −0.87 ± 0.03. The vertical scale heights in NGC 4631 vary significantly in different regions within the galaxy and their mean values at 4.85 GHz are with 2.3 kpc (370 pc) for the thick (thin) disk higher than the mean values found so far in six other edge-on spiral galaxies. This may originate in the tidal interaction of NGC 4631 with its neighbouring galaxies. The rotation measures are characterized by a smooth large-scale distribution. Along the galactic plane the degree of Faraday depolarization is significantly high. We estimated a total magnetic field strength in the disk of NGC 4631 of B t ≈ 9 ± 2 μG and an ordered field strength of B ord ≈ 2 ± 1 μG. The total field strengths in the halo are of the order of the total magnetic field strength in the disk, whereas the ordered field strengths in the halo seem to be higher than the value in the disk. Conclusions. The derived distribution of rotation measures implies that NGC 4631 has a large-scale regular magnetic field configuration. Despite the strong Faraday depolarization along the galactic plane and the strong beam depolarization in the transition zone between the disk and halo, our research strongly indicates that the magnetic field orientation along the central 5-7 kpc of the disk is also plane-parallel. Therefore, we claim that NGC 4631 also has a magnetic field structure plane-parallel along its entire disk, similar to all other edge-on galaxies observed up to now.

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The Polarization of Cosmic Radio Waves

Cited by 153 publications

References 0 publications

A View through Faraday’s Fog. II. Parsec‐Scale Rotation Measures in 40 Active Galactic Nuclei

A View through Faraday’s Fog. II. Parsec‐Scale Rotation Measures in 40 Active Galactic Nuclei

JVLA S- and X-band polarimetry of the merging cluster Abell 2256

Magnetic field structure and halo in NGC 4631

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