scholarly journals Magnetic Field Strengths in the Hot Spots and Lobes of Three Powerful Fanaroff‐Riley Type II Radio Sources

2002 ◽  
Vol 581 (2) ◽  
pp. 948-973 ◽  
Author(s):  
M. J. Hardcastle ◽  
M. Birkinshaw ◽  
R. A. Cameron ◽  
D. E. Harris ◽  
L. W. Looney ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Hot Spots ◽  
Radio Sources ◽  
Type Ii ◽  
Field Strengths

scholarly journals Magnetic Field Strengths of GPS Radio Sources

1999 ◽  
Vol 194 ◽  
pp. 324-326
Author(s):  
V. G. Panajyan
Keyword(s):  
Magnetic Field ◽  
High Frequency ◽  
Radio Sources ◽  
Spectral Indices ◽  
The Past ◽  
Spectrum Radio ◽  
Field Strengths

GHz peaked spectrum radio sources (GPS) are believed to be a subclass of compact steep spectrum radio sources (CSS) with high frequency spectral indices α < −0.5 (5 ˜ vα), linear sizes of pc to kpc scale and turnover spectra near 1GHz. Due to the work of many radioastronomers during the past two decades many properties of CSS and GPS radio sources at present are known (O'Dea,C.P. et al.1998, and references therein).

scholarly journals Extragalactic megahertz-peaked spectrum radio sources at milliarcsecond scales

2019 ◽  
Vol 628 ◽  
pp. A56 ◽  
Author(s):  
M. A. Keim ◽  
J. R. Callingham ◽  
H. J. A. Röttgering
Keyword(s):  
Magnetic Field ◽  
Spectral Characteristics ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
Spectrum Radio ◽  
Spectral Peaks ◽  
Murchison Widefield Array ◽  
Very Long Baseline Array ◽  
Field Strengths

Extragalactic peaked-spectrum radio sources are thought to be the progenitors of larger, radio-loud active galactic nuclei (AGN). Synchrotron self-absorption (SSA) has often been identified as the cause of their spectral peak. The identification of new megahertz-peaked spectrum sources from the GaLactic and Extragalactic All-sky Murchison Widefield Array (GLEAM) survey provides an opportunity to test how radio sources with spectral peaks below 1 GHz fit within this evolutionary picture. We observed six peaked-spectrum sources selected from the GLEAM survey, three that have spectral characteristics which violate SSA and three that have spectral peaks below 230 MHz, with the Very Long Baseline Array at 1.55 and 4.96 GHz. We present milliarcsecond resolution images of each source and constrain their morphology, linear size, luminosity, and magnetic field strength. Of the sources that are resolved by our study, the sources that violate SSA appear to be compact doubles, while the sources with peak frequencies below 230 MHz have core-jet features. We find that all of our sources are smaller than expected from SSA by factors of ≳20. We also find that component magnetic field strengths calculated from SSA are likely inaccurate, differing by factors of ≳5 from equipartition estimates. The calculated equipartition magnetic field strengths more closely resemble estimates from previously studied gigahertz-peaked spectrum sources. Exploring a model of the interaction between jets and the interstellar medium, we demonstrate that free-free absorption (FFA) can accurately describe the linear sizes and peak frequencies of our sources. Our findings support the theory that there is a fraction of peaked-spectrum sources whose spectral peaks are best modeled by FFA, implying our understanding of the early stages of radio AGN is incomplete.

scholarly journals Magnetic Fields & Ionized Gas in Elliptical Galaxy Halos

1990 ◽  
Vol 140 ◽  
pp. 459-462
Author(s):  
Richard G. Strom
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Elliptical Galaxy ◽  
Radio Sources ◽  
Early Type ◽  
Ionized Gas ◽  
X Ray ◽  
Galaxy Halos ◽  
Field Strengths

Faraday depolarization estimates of thermal densities within the components of double radio sources agree well with estimates from X-ray observations of hot halos around early-type galaxies, provided magnetic field strengths are close to their equipartition values. Internal Faraday dispersion is the main cause of the depolarization observed.

scholarly journals Constraints on the Cluster Environments and Hot Spot Magnetic Field Strengths of the Radio Sources 3C 280 and 3C 254

2003 ◽  
Vol 584 (2) ◽  
pp. 643-656 ◽  
Author(s):  
Megan Donahue ◽  
Ruth A. Daly ◽  
Donald J. Horner
Keyword(s):  
Magnetic Field ◽  
Hot Spot ◽  
Radio Sources ◽  
Field Strengths

scholarly journals An X‐Ray Study of Magnetic Field Strengths and Particle Content in the Lobes of FR II Radio Sources

2005 ◽  
Vol 626 (2) ◽  
pp. 733-747 ◽  
Author(s):  
J. H. Croston ◽  
M. J. Hardcastle ◽  
D. E. Harris ◽  
E. Belsole ◽  
M. Birkinshaw ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Radio Sources ◽  
Particle Content ◽  
X Ray ◽  
Field Strengths

scholarly journals [ITAL]Chandra[/ITAL] Observations of Cygnus A: Magnetic Field Strengths in the Hot Spots of a Radio Galaxy

2000 ◽  
Vol 544 (1) ◽  
pp. L27-L30 ◽  
Author(s):  
A. S. Wilson ◽  
A. J. Young ◽  
P. L. Shopbell
Keyword(s):  
Magnetic Field ◽  
Hot Spots ◽  
Radio Galaxy ◽  
Cygnus A ◽  
Field Strengths

scholarly journals Hot-Spots in Luminous Extragalactic Radio Sources

1982 ◽  
Vol 97 ◽  
pp. 161-162 ◽  
Author(s):  
R. A. Laing
Keyword(s):  
Magnetic Field ◽  
Hot Spots ◽  
Hot Spot ◽  
Leading Edge ◽  
Active Regions ◽  
Radio Sources ◽  
List Type ◽  
Inversion Symmetry ◽  
Extragalactic Radio Sources ◽  
Radio Lobe

Compact hot-spots in luminous extragalactic radio sources are often double on the scale of a few kpc (Laing 1981a). Examples are shown in Figures 1–3; the maps were made with the A and B configurations of the VLA. The general features are as follows: (a)It is usually possible to recognize a compact, “active” subcomponent within a radio lobe. This has a size of <1 kpc and may only contain a small fraction of the total flux of the hot-spot. It need not be at the leading edge.(b)More diffuse regions are often grossly offset from the source axis (e.g. 3C 196). In some cases, there is apparent inversion symmetry about the optical identification.(c)The characteristic morphology of a diffuse subcomponent is best illustrated by the eastern hot-spot of 3C 20, which is limb-brightened, with a circumferential magnetic field. The bright edge is on the side furthest away from the compact subcomponent.(d)The polarization structure in the diffuse subcomponents, like that in most extended radio lobes, can be explained if the magnetic field has been sheared so as to be tangential to the surface, but is otherwise random (Laing 1980; 1981b).(e)The most obvious explanation for the multiple structure is that the compact subcomponents represent the points of impact on the surrounding gas of twin beams from the associated galactic nucleus; if these alter their direction, then diffuse remnants may be formed. This idea would be consistent with the inversion symmetry seen, for example, in 3C 196.(f)A problem with this model is posed by the detailed morphology of the diffuse subcomponents: why should the bright limb be opposite the compact subcomponent, rather than at the leading edge of the source? An alternative picture, in which the diffuse subcomponents are formed by material escaping from the active regions, should also be considered.

scholarly journals Time-Variations of 17GHz Radio Bursts by Multi-Source Structures

1980 ◽  
Vol 86 ◽  
pp. 131-134
Author(s):  
Takeo Kosugi
Keyword(s):  
Magnetic Field ◽  
Point Of View ◽  
Radio Sources ◽  
Radio Bursts ◽  
Type Ii ◽  
Type Iii ◽  
Type Iv ◽  
Long Duration ◽  
Time Variations ◽  
Lines Of Force

Four multi-source radio bursts observed with the new 17GHz interferometer at Nobeyama are analyzed and presented from the point of view of their time-variations.Three of them (Sep. 6, 1978; Oct. 9, 1978; and Feb. 17, 1979) were essentially of an impulsive nature and all showed distinct double-source structures. Their polarization structures and time-variations are discussed and compared with type III and type II burst occurrences. The results of the comparison suggest either that electron accelerating regions moved across magnetic lines of force or that a rapid magnetic field rearrangement occurred near an accelerating region.A quite different type of multi-source radio bursts was observed on Nov.10,1978. It had a long duration of several hours and was associated with type IV bursts at metric and decimetric wavelengths. At least five radio sources were observed to appear at 17GHz. A detailed description of this event is presented in comparison with the evolution of both Hα-flare and type IV bursts.

Magnetic-field strengths from optical polarization data

1967 ◽  
Vol 31 ◽  
pp. 381-383
Author(s):  
J. M. Greenberg
Keyword(s):  
Magnetic Field ◽  
Optical Polarization ◽  
Polarization Data ◽  
Term Model ◽  
Source Of Information ◽  
Field Strengths

Van de Hulst (Paper 64, Table 1) has marked optical polarization as a questionable or marginal source of information concerning magnetic field strengths. Rather than arguing about this–I should rate this method asq+-, or quarrelling about the term ‘model-sensitive results’, I wish to stress the historical point that as recently as two years ago there were still some who questioned that optical polarization was definitely due to magnetically-oriented interstellar particles.

Radio Measurements of Coronal Magnetic Fields

1994 ◽  
Vol 144 ◽  
pp. 21-28 ◽  
Author(s):  
G. B. Gelfreikh
Keyword(s):  
Magnetic Field ◽  
Magnetic Fields ◽  
Solar Corona ◽  
Active Regions ◽  
High Sensitivity ◽  
Coronal Magnetic Field ◽  
Transverse Magnetic ◽  
Radio Sources ◽  
Radio Waves ◽  
Solar Active Regions

AbstractA review of methods of measuring magnetic fields in the solar corona using spectral-polarization observations at microwaves with high spatial resolution is presented. The methods are based on the theory of thermal bremsstrahlung, thermal cyclotron emission, propagation of radio waves in quasi-transverse magnetic field and Faraday rotation of the plane of polarization. The most explicit program of measurements of magnetic fields in the atmosphere of solar active regions has been carried out using radio observations performed on the large reflector radio telescope of the Russian Academy of Sciences — RATAN-600. This proved possible due to good wavelength coverage, multichannel spectrographs observations and high sensitivity to polarization of the instrument. Besides direct measurements of the strength of the magnetic fields in some cases the peculiar parameters of radio sources, such as very steep spectra and high brightness temperatures provide some information on a very complicated local structure of the coronal magnetic field. Of special interest are the results found from combined RATAN-600 and large antennas of aperture synthesis (VLA and WSRT), the latter giving more detailed information on twodimensional structure of radio sources. The bulk of the data obtained allows us to investigate themagnetospheresof the solar active regions as the space in the solar corona where the structures and physical processes are controlled both by the photospheric/underphotospheric currents and surrounding “quiet” corona.

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