Very long baseline interferometry polarization studies of quasars and active galactic nuclei

1986 ◽  
Vol 64 (4) ◽  
pp. 434-439 ◽  
Author(s):  
J. F. C. Wardle ◽  
D. H. Roberts
Keyword(s):  
Active Galactic Nuclei ◽  
Linear Polarization ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Sources ◽  
Long Baseline ◽  
First Results ◽  
Polarization Studies ◽  
Theoretical Issues

We present some first results of a program to map the distribution of linear polarization in compact radio sources with milliarcsecond resolution. We show first-epoch maps of 3C345 and 0735 + 178 and first- and second-epoch maps of OJ287. In general, the polarization is mainly associated with optically thin (jet) components. In the case of OJ287, polarization maps made 1 year apart are strikingly different. We also discuss some of the theoretical issues raised by these observations.

scholarly journals High-resolution radio astronomy: An outlook for Africa

2019 ◽  
Vol 15 (S356) ◽  
pp. 137-142
Author(s):  
Leonid I. Gurvits ◽  
Robert Beswick ◽  
Melvin Hoare ◽  
Ann Njeri ◽  
Jay Blanchard ◽  
...  
Keyword(s):  
Active Galactic Nuclei ◽  
Structural Changes ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
High Sensitivity ◽  
Radio Sources ◽  
Long Baseline ◽  
The World ◽  
The Status ◽  
Near Term

AbstractVery Long Baseline Interferometry (VLBI) offers unrivalled resolution in studies of celestial radio sources. The subjects of interest of the current IAU Symposium, the Active Galactic Nuclei (AGN) of all types, constitute the major observing sample of modern VLBI networks. At present, the largest in the world in terms of the number of telescopes and geographical coverage is the European VLBI Network (EVN), which operates under the “open sky” policy via peer-reviewed observing proposals. Recent EVN observations cover a broad range of science themes from high-sensitivity monitoring of structural changes in inner AGN areas to observations of tidal eruptions in AGN cores and investigation of redshift-dependent properties of parsec-scale radio structures of AGN. All the topics above should be considered as potentially rewarding scientific activities of the prospective African VLBI Network (AVN), a natural “scientific ally” of EVN. This contribution briefly describe the status and near-term strategy for the AVN development as a southern extension of the EVN-AVN alliance and as an eventual bridge to the Square Kilometre Array (SKA) with its mid-frequency core in South Africa.

scholarly journals Core-shifts and proper-motion constraints in the S5 polar cap sample at the 15 and 43 GHz bands

2018 ◽  
Vol 614 ◽  
pp. A74 ◽  
Author(s):  
F. J. Abellán ◽  
I. Martí-Vidal ◽  
J. M. Marcaide ◽  
J. C. Guirado
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Polar Cap ◽  
Motion Constraints ◽  
The Core ◽  
Long Baseline ◽  
Precision Phase ◽  
First Time ◽  
Core Shift

We have studied a complete radio sample of active galactic nuclei with the very-long-baseline-interferometry (VLBI) technique and for the first time successfully obtained high-precision phase-delay astrometry at Q band (43 GHz) from observations acquired in 2010. We have compared our astrometric results with those obtained with the same technique at U band (15 GHz) from data collected in 2000. The differences in source separations among all the source pairs observed in common at the two epochs are compatible at the 1σ level between U and Q bands. With the benefit of quasi-simultaneous U and Q band observations in 2010, we have studied chromatic effects (core-shift) at the radio source cores with three different methods. The magnitudes of the core-shifts are of the same order (about 0.1 mas) for all methods. However, some discrepancies arise in the orientation of the core-shifts determined through the different methods. In some cases these discrepancies are due to insufficient signal for the method used. In others, the discrepancies reflect assumptions of the methods and could be explained by curvatures in the jets and departures from conical jets.

scholarly journals The Milliarcsecond Structure of Active Galactic Nuclei Observed with VLBI

1989 ◽  
Vol 134 ◽  
pp. 525-528
Author(s):  
T. J. Pearson ◽  
A. C. S. Readhead
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Relativistic Motion ◽  
Powerful Radio ◽  
Long Baseline ◽  
Vlbi Observations ◽  
Central Engine

Very Long Baseline Interferometry at radio wavelengths is the only technique available for imaging the central few parsecs of powerful radio galaxies and quasars. VLBI observations have shown that in many nuclei radio-emitting material is collimated into a jet on a scale less than a parsec and ejected at relativistic velocities. The interpretation of the observations is complicated by the relativistic motion, however: the images are dominated by those parts of the source that are moving almost directly towards the observer, and thus amplified by relativistic aberration. Nonetheless, the VLBI images are vital for understanding the nature of the central engine, the cause of the collimation, and the physics of the jets.

scholarly journals Polarisation Characteristics and Variability of the Compact Radio Structures of AGN

2002 ◽  
Vol 19 (1) ◽  
pp. 147-151 ◽  
Author(s):  
Denise C. Gabuzda
Keyword(s):  
Magnetic Field ◽  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Long Baseline ◽  
Polarisation Measurements

AbstractVery long baseline interferometry (VLBI) polarisation measurements provide information about the parsec-scale magnetic field structures in compact active galactic nuclei (AGN), as well as the densities of relativistic and thermal electrons in the radio emitting regions. This paper reviews the role of polarisation VLBI in studies of AGN variability on both relatively long and short (intraday) timescales.

scholarly journals Jets in AGN at extremely high redshifts

2014 ◽  
Vol 10 (S313) ◽  
pp. 327-328
Author(s):  
Leonid I. Gurvits ◽  
Sándor Frey ◽  
Zsolt Paragi
Keyword(s):  
Black Hole ◽  
Active Galactic Nuclei ◽  
Plasma Flow ◽  
Very Long Baseline Interferometry ◽  
Angular Resolution ◽  
Galactic Nuclei ◽  
Physical Parameters ◽  
Long Baseline ◽  
General Terms ◽  
Jet Structure

The jet phenomenon is a trademark of active galactic nuclei (AGN). In most general terms, the current understanding of this phenomenon explains the jet appearance by effects of relativistic plasma physics. The fundamental source of energy that feeds the plasma flow is believed to be the gravitational field of a central supermassive black hole. While the mechanism of energy transfer and a multitude of effects controlling the plasma flow are yet to be understood, major properties of jets are strikingly similar in a broad range of scales from stellar to galactic. They are supposed to be controlled by a limited number of physical parameters, such as the mass of a central black hole and its spin, magnetic field induction and accretion rate. In a very simplified sense, these parameters define the formation of a typical core–jet structure observed at radio wavelengths in the region of the innermost central tens of parsecs in AGN. These core–jet structures are studied in the radio domain by Very Long Baseline Interferometry (VLBI) with milli- and sub-milliarcsecond angular resolution. Such structures are detectable at a broad range of redshifts. If observed at a fixed wavelength, a typical core–jet AGN morphology would appear as having a steep-spectrum jet fading away with the increasing redshift while a flat-spectrum core becoming more dominant. If core–jet AGN constitute the same population of objects throughout the redshift space, the apparent “prominence” of jets at higher redshifts must decrease (Gurvits 1999): well pronounced jets at high z must appear less frequent than at low z.

scholarly journals Global alignments of parsec-scale AGN radio jets and their polarization planes

2020 ◽  
Vol 635 ◽  
pp. A102 ◽  
Author(s):  
D. Blinov ◽  
C. Casadio ◽  
N. Mandarakas ◽  
E. Angelakis
Keyword(s):  
Active Galactic Nuclei ◽  
Large Scale ◽  
Very Long Baseline Interferometry ◽  
Parallel Transport ◽  
Polarization Plane ◽  
Galactic Nuclei ◽  
Radio Jets ◽  
Long Baseline ◽  
Flux Density Distribution ◽  
First Time

Context. A number of works have reported that the polarization plane of extragalactic sources as well as the structural axes of radio sources are aligned on the large scale. However, both the claims and their interpretation remain controversial. Aims. For the first time, we explore the alignment of parsec-scale jets. Additionally, we use archival polarimetric data at different wavelengths in order to compare the relative orientations of the jets and the polarization planes of their emission. Methods. Using the flux density distribution in very long baseline interferometry radio maps from the Astrogeo database, we determine the parsec-scale jet orientation for the largest sample of active galactic nuclei to date. Employing the method of parallel transport and a sample statistics characterizing the jet orientation dispersion among neighbors, we test whether the identified jets are significantly aligned. Results. We show that the parsec-scale jets in our sample do not demonstrate any significant global alignments. Moreover, the jet direction is found to be weakly correlated with the direction of the polarization plane at different frequencies.

scholarly journals The VSOP project: Space VLBI Imaging of AGN at 1.6 and 5 GHz

2001 ◽  
Vol 205 ◽  
pp. 118-121
Author(s):  
Y. Murata ◽  
H. Hirabayashi ◽  
P.G. Edwards
Keyword(s):  
Active Galactic Nuclei ◽  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Radio Telescopes ◽  
Space Observatory ◽  
Long Baseline ◽  
5 Ghz

The VLBI Space Observatory Programme (VSOP) combines an orbiting radiotelescope with arrays of ground radio telescopes to extend the Very Long Baseline Interferometry (VLBI) technique to baselines up to almost three Earth diameters. In this paper, we present results from VSOP observations of active galactic nuclei (AGN) at 1.6 and 5 GHz from the first 3.5 years of the mission.

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