Small-scale variations in the galactic magnetic field - The rotation measure structure function and birefringence in interstellar scintillations

1984 ◽  
Vol 284 ◽  
pp. 126 ◽  
Author(s):  
J. H. Simonetti ◽  
J. M. Cordes ◽  
S. R. Spangler
Keyword(s):  
Magnetic Field ◽  
Structure Function ◽  
Small Scale ◽  
Galactic Magnetic Field ◽  
Rotation Measure

Fluctuations in the Galactic Magnetic Field

1990 ◽  
Vol 140 ◽  
pp. 55-58
Author(s):  
James M. Cordes ◽  
Andrew Clegg ◽  
John Simonetti
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Measure Data ◽  
Small Scale ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Rotation Measure ◽  
Scale Field ◽  
Large Scale Field ◽  
The Magnetic Field

We discuss small scale structure in the Galactic magnetic field as inferred from Faraday rotation measurements of extragalactic radio sources. The rotation measure data suggest a continuum of length scales extending from parsec scales down to at least 0.01 pc and perhaps to as small as 109 cm. Such turbulence in the magnetic field comprises a reservoir of energy that is comparable to the energy in the large scale field.

scholarly journals The Rotation Measure of Background Radio Sources Seen Through the Supernova Remnant OA184 (G166.2+2.5)

1988 ◽  
Vol 101 ◽  
pp. 355-358
Author(s):  
K.-T. Kim ◽  
P.P. Kronberg ◽  
T.L. Landecker
Keyword(s):  
Magnetic Field ◽  
Supernova Remnant ◽  
Active Plasma ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Rotation Measure ◽  
Polarity Change ◽  
Larger Sample

AbstractRadio sources in the field of the extended SNR OA184 (G166.2+2.5) have been studied to determine the excess rotation measure (RM) arising from the SNR. Of a total of 32 radio sources observed with the VLA in the C configuration, eight are found to be polarized above 7σ The sources seen through the SNR show significantly high RM in comparison to background sources. The excess RM due to the Faraday active plasma in the SNR is estimated to be 150±20 rad m−2, which corresponds to . The sign of RMs of the sources within an area of about 2°×2° centred on the SNR shows a systematic longitudinal polarity change on either side of l ≈ 166°.2. Although a larger sample is needed to justify this, we tentatively interpret this “flip” as due to the reversal of an irregular component of the galactic magnetic field on a scale of order 100 pc.

scholarly journals F. Magnetic Fields, Pulsars, X-Ray And Gamma-Ray Emission

1985 ◽  
Vol 19 (1) ◽  
pp. 431-435
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Gamma Ray ◽  
Logarithmic Spiral ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Rotation Measure ◽  
The Galaxy ◽  
Magnetic Field Model ◽  
Characteristic Features

During the triennium under review many papers reported on studies of the structure of the galactic magnetic field. Andreasyan used rotation measures (RM) of large samples of extra-galactic radio sources and pulsars (29.156.001) or radio sources (32.156.002), and Inoue and Tabara (31.156.011) used in addition optical polarization of stars to investigate the direction of the large-scale regular magnetic field. Thomson and Nelson analyse the RMs of 459 extragalactic sources (32. 161.001) to determine the best fit parameters for a galactic magnetic-field model, and find agreement with their earlier work using pulsars (27.156.009). Similarly, Sofue and Fujimoto (33.155.011) show that the characteristic features of the RM distribution on the sky are well reproduced by a model in which the magnetic field is in a bisymmetric, two-armed logarithmic spiral configuration. Finally, Welter, Perry and Kronberg (37.159.096) present a statistical analysis of the (Galaxy-corrected) residual rotation measure (RRM) of 116 QSOs.

scholarly journals The Production of Rotation Measure Gradients in the Lobes of Extragalactic Radio Sources

1990 ◽  
Vol 140 ◽  
pp. 477-481
Author(s):  
G.V. Bicknell ◽  
R.A. Cameron ◽  
R.A. Gingold
Keyword(s):  
Magnetic Field ◽  
Surrounding Medium ◽  
Small Scale ◽  
Radio Sources ◽  
Large Rotation ◽  
Extragalactic Radio Sources ◽  
Cygnus A ◽  
Rotation Measure ◽  
Order Of Magnitude ◽  
Scale Turbulence

It is proposed that the large rotation measure gradients observed in the lobes of some extragalactic radio sources are produced by non–linear Kelvin–Helmholtz surface waves. Related small scale turbulence is responsible for a “diffuse spray” of relativistic plasma and magnetic field into the surrounding medium. The mixture of magnetic field and thermal plasma causes large rotation measure variations on the scale of the Kelvin–Helmholtz waves. An order of magnitude prediction of the effect is in good agreement with the observations of Cygnus A and PKS 2104–25 N.

scholarly journals Helical magnetic fields in molecular clouds?

2018 ◽  
Vol 614 ◽  
pp. A100 ◽  
Author(s):  
M. Tahani ◽  
R. Plume ◽  
J. C. Brown ◽  
J. Kainulainen
Keyword(s):  
Magnetic Field ◽  
Star Formation ◽  
Magnetic Fields ◽  
Molecular Clouds ◽  
Column Density ◽  
Measure Data ◽  
Line Of Sight ◽  
Small Scale ◽  
Rotation Measure ◽  
Data Points

Context. Magnetic fields pervade in the interstellar medium (ISM) and are believed to be important in the process of star formation, yet probing magnetic fields in star formation regions is challenging. Aims. We propose a new method to use Faraday rotation measurements in small-scale star forming regions to find the direction and magnitude of the component of magnetic field along the line of sight. We test the proposed method in four relatively nearby regions of Orion A, Orion B, Perseus, and California. Methods. We use rotation measure data from the literature. We adopt a simple approach based on relative measurements to estimate the rotation measure due to the molecular clouds over the Galactic contribution. We then use a chemical evolution code along with extinction maps of each cloud to find the electron column density of the molecular cloud at the position of each rotation measure data point. Combining the rotation measures produced by the molecular clouds and the electron column density, we calculate the line-of-sight magnetic field strength and direction. Results. In California and Orion A, we find clear evidence that the magnetic fields at one side of these filamentary structures are pointing towards us and are pointing away from us at the other side. Even though the magnetic fields in Perseus might seem to suggest the same behavior, not enough data points are available to draw such conclusions. In Orion B, as well, there are not enough data points available to detect such behavior. This magnetic field reversal is consistent with a helical magnetic field morphology. In the vicinity of available Zeeman measurements in OMC-1, OMC-B, and the dark cloud Barnard 1, we find magnetic field values of − 23 ± 38 μG, − 129 ± 28 μG, and 32 ± 101 μG, respectively, which are in agreement with the Zeeman measurements.

scholarly journals Pulsars as Probes of the Galactic Magnetic Field

1990 ◽  
Vol 140 ◽  
pp. 41-43
Author(s):  
A. G. Lyne
Keyword(s):  
Magnetic Field ◽  
Faraday Rotation ◽  
Linear Polarization ◽  
Dispersion Measure ◽  
Radio Sources ◽  
Galactic Magnetic Field ◽  
Pulsar Emission ◽  
Pulsar Radiation ◽  
Rotation Measure

The high linear polarization of pulsar radiation allows a reasonably easy determination of the Faraday rotation measure. Unlike other radio sources, the impulsive nature of pulsar emission also permits a determination of the number of electrons responsible for the rotation, through the dispersion measure, DM.

scholarly journals The intergalactic magnetic field probed by a giant radio galaxy

2019 ◽  
Vol 622 ◽  
pp. A16 ◽  
Author(s):  
S. P. O’Sullivan ◽  
J. Machalski ◽  
C. L. Van Eck ◽  
G. Heald ◽  
M. Brüggen ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Large Scale ◽  
Radio Galaxy ◽  
Small Scale ◽  
Cosmological Simulations ◽  
Rotation Measure ◽  
Sky Survey ◽  
Intergalactic Magnetic Field ◽  
Using Data ◽  
The Universe

Cosmological simulations predict that an intergalactic magnetic field (IGMF) pervades the large scale structure (LSS) of the Universe. Measuring the IGMF is important to determine its origin (i.e. primordial or otherwise). Using data from the LOFAR Two Metre Sky Survey (LoTSS), we present the Faraday rotation measure (RM) and depolarisation properties of the giant radio galaxy J1235+5317, at a redshift of z = 0.34 and 3.38 Mpc in size. We find a mean RM difference between the lobes of 2.5 ± 0.1 rad m−2, in addition to small scale RM variations of ∼0.1 rad m−2 . From a catalogue of LSS filaments based on optical spectroscopic observations in the local universe, we find an excess of filaments intersecting the line of sight to only one of the lobes. Associating the entire RM difference to these LSS filaments leads to a gas density-weighted IGMF strength of ∼0.3 μG. However, direct comparison with cosmological simulations of the RM contribution from LSS filaments gives a low probability (∼5%) for an RM contribution as large as 2.5 rad m−2, for the case of IGMF strengths of 10–50 nG. It is likely that variations in the RM from the Milky Way (on 11′ scales) contribute significantly to the mean RM difference, and a denser RM grid is required to better constrain this contribution. In general, this work demonstrates the potential of the LOFAR telescope to probe the weak signature of the IGMF. Future studies, with thousands of sources with high accuracy RMs from LoTSS, will enable more stringent constraints on the nature of the IGMF.

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