scholarly journals Opacity, variability, and kinematics of AGN jets

2019 ◽  
Vol 486 (1) ◽  
pp. 430-439 ◽  
Author(s):  
A M Kutkin ◽  
I N Pashchenko ◽  
K V Sokolovsky ◽  
Y Y Kovalev ◽  
M F Aller ◽  
...  
Keyword(s):  
Time Delay ◽  
Gaussian Process Regression ◽  
Lorentz Factor ◽  
Time Lags ◽  
The Core ◽  
Long Baseline ◽  
Dependent Change ◽  
Bulk Motion ◽  
Shift Effect ◽  
Core Shift

ABSTRACT Synchrotron self-absorption in active galactic nuclei (AGN) jets manifests itself as a time delay between flares observed at high and low radio frequencies. It is also responsible for the observing frequency-dependent change in size and position of the apparent base of the jet, aka the core shift effect, detected with very long baseline interferometry (VLBI). We measure the time delays and the core shifts in 11 radio-loud AGN to estimate the speed of their jets without relying on multi-epoch VLBI kinematics analysis. The 15–8 GHz total flux density time lags are obtained using Gaussian process regression, the core shift values are measured using VLBI observations and adopted from the literature. A strong correlation is found between the apparent core shift and the observed time delay. Our estimate of the jet speed is higher than the apparent speed of the fastest VLBI components by the median coefficient of 1.4. The coefficient ranges for individual sources from 0.5 to 20. We derive Doppler factors, Lorentz factors, and viewing angles of the jets, as well as the corresponding de-projected distance from the jet base to the core. The results support evidence for acceleration of the jets with bulk motion Lorentz factor Γ ∝ R0.52±0.03 on de-projected scales R of 0.5–500 parsecs.

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 first estimate of radio jet proper motion at z > 5

2014 ◽  
Vol 446 (3) ◽  
pp. 2921-2928 ◽  
Author(s):  
Sándor Frey ◽  
Zsolt Paragi ◽  
Judit O. Fogasy ◽  
Leonid I. Gurvits
Keyword(s):  
High Redshift ◽  
Spectral Energy Distribution ◽  
Lorentz Factor ◽  
Spectral Energy ◽  
Dual Frequency ◽  
The Core ◽  
Long Baseline ◽  
Large Bulk ◽  
5 Ghz ◽  
Jet Structure

Abstract The extremely high-redshift (z = 5.3) radio source SDSS J102623.61+254259.5 (J1026+2542) is among the most distant and most luminous radio-loud active galactic nuclei (AGN) known to date. Its one-sided radio jet structure on milliarcsecond (mas) and ∼10-mas scales typical for blazars was first imaged at 5 GHz with very long baseline interferometry (VLBI) in 2006. Here we report on our dual-frequency (1.7 and 5 GHz) imaging observations performed with the European VLBI Network (EVN) in 2013. The prominent jet structure allows us to identify individual components whose apparent displacement can be detected over the time span of 7.33 yr. This is the first time when jet proper motions are directly derived in a blazar at z > 5. The small values of up to ∼0.1 mas yr−1 are consistent with what is expected in a relativistic cosmological model if redshift is a measure of distance. The apparent superluminal jet speeds, considered tentative because derived from two epochs only, exceed 10 c for three different components along the jet. Based on modelling its spectral energy distribution, J1026+2542 is known to have its X-ray jet oriented close to the line of sight, with significant Doppler boosting and a large bulk Lorentz factor (Γ ≈ 13). The new VLBI observations, indicating ∼2.3 × 1012 K lower limit to the core brightness temperature, are consistent with this picture. The spectral index in the core region is −0.35.

scholarly journals Opacity in compact extragalactic radio sources and the core shift effect

2008 ◽  
Vol 131 ◽  
pp. 012058
Author(s):  
Y Y Kovalev ◽  
A P Lobanov ◽  
A B Pushkarev ◽  
J A Zensus
Keyword(s):  
Radio Sources ◽  
Extragalactic Radio Sources ◽  
The Core ◽  
Shift Effect ◽  
Core Shift

scholarly journals The core shift effect in the blazar 3C 454.3

2013 ◽  
Vol 437 (4) ◽  
pp. 3396-3404 ◽  
Author(s):  
A. M. Kutkin ◽  
K. V. Sokolovsky ◽  
M. M. Lisakov ◽  
Y. Y. Kovalev ◽  
T. Savolainen ◽  
...  
Keyword(s):  
The Core ◽  
Shift Effect ◽  
Core Shift

scholarly journals A bias in VLBI measurements of the core shift effect in AGN jets

2020 ◽  
Vol 499 (3) ◽  
pp. 4515-4525
Author(s):  
I N Pashchenko ◽  
A V Plavin ◽  
A M Kutkin ◽  
Y Y Kovalev
Keyword(s):  
Approximation Error ◽  
Radial Distance ◽  
Galactic Nuclei ◽  
Image Resolution ◽  
Data Sets ◽  
Model Approximation ◽  
The Core ◽  
Vlbi Data ◽  
Shift Effect ◽  
Core Shift

ABSTRACT The Blandford and Königl model of active galactic nuclei (AGN) jets predicts that the position of the apparent opaque jet base – the core – changes with frequency. This effect is observed with radio interferometry and is widely used to infer parameters and structure of the innermost jet regions. The position of the radio core is typically estimated by fitting a Gaussian template to the interferometric visibilities. This results in a model approximation error, i.e. a bias that can be detected and evaluated through simulations of observations with a realistic jet model. To assess the bias, we construct an artificial sample of sources based on the AGN jet model evaluated on a grid of the parameters derived from a real VLBI flux-density-limited sample and create simulated VLBI data sets at 2.3, 8.1, and 15.4 GHz. We found that the core position shifts from the true jet apex are generally overestimated. The bias is typically comparable to the core shift random error and can reach a factor of 2 for jets with large apparent opening angles. This observational bias depends mostly on the ratio between the true core shift and the image resolution. This implies that the magnetic field, the core radial distance, and the jet speed inferred from the core shift measurements are overestimated. We present a method to account for the bias.

scholarly journals MEASURING THE CORE SHIFT EFFECT IN AGN JETS WITH THE EXTENDED KOREAN VLBI NETWORK

2015 ◽  
Vol 48 (5) ◽  
pp. 277-284 ◽  
Author(s):  
TAEHYUN JUNG ◽  
RICHARD DODSON ◽  
SEOG-TAE HAN ◽  
MARIA J. RIOJA ◽  
DO-YOUNG BYUN ◽  
...  
Keyword(s):  
The Core ◽  
Shift Effect ◽  
Core Shift

scholarly journals Studies of stationary features in jets: BL Lacertae

2020 ◽  
Vol 640 ◽  
pp. A62
Author(s):  
T. G. Arshakian ◽  
A. B. Pushkarev ◽  
M. L. Lister ◽  
T. Savolainen
Keyword(s):  
Time Scales ◽  
Stable State ◽  
Brightness Distribution ◽  
Transverse Waves ◽  
Bl Lacertae ◽  
The Core ◽  
Long Baseline ◽  
Core Shift ◽  
Stationary Component ◽  
Jet Axis

Context. Monitoring of BL Lacertae at 15 GHz with the Very Long Baseline Array (VLBA) has revealed a quasi-stationary radio feature in the innermost part of the jet, at 0.26 mas from the radio core. Stationary features are found in many blazars, but they have rarely been explored in detail. Aims. We aim to study the kinematics, dynamics, and brightness of the quasi-stationary feature of the jet in BL Lacertae based on VLBA monitoring with submilliarcsecond resolution (subparsec-scales) over 17 years. Methods. We analysed position uncertainties and flux leakage effects of the innermost quasi-stationary feature and developed statistical tools to distinguish the motions of the stationary feature and the radio core. We constructed a toy model to simulate the observed emission of the quasi-stationary component. Results. We find that trajectories of the quasi-stationary component are aligned along the jet axis, which can be interpreted as evidence of the displacements of the radio core. The intrinsic motions of the core and quasi-stationary component have a commensurate contribution to the apparent motion of the stationary component. During the jet-stable state, the core shift significantly influences the apparent displacements of the stationary component, which shows orbiting motion with reversals. The quasi-stationary component has low superluminal speeds on time scales of months. On time-scales of few years, the apparent mean speeds are subrelativistic, of about 0.15 the speed of light. We find that the brightness profile of the quasi-stationary component is asymmetric along and transverse to the jet axis, and this effect remains unchanged regardless of epoch. Conclusions. Accurate positional determination, a high cadence of observations, and a proper accounting for the core shift are crucial for the measurement of the trajectories and speeds of the quasi-stationary component. Its motion is similar to the behaviour of the jet nozzle, which drags the outflow in a swinging motion and excites transverse waves of different amplitudes travelling downstream. A simple modelling of the brightness distribution shows that the configuration of twisted velocity field formed at the nozzle of the jet in combination with small jet viewing angle can account for the observed brightness asymmetry.

scholarly journals A VLBA survey of the core shift effect in AGN jets

2011 ◽  
Vol 532 ◽  
pp. A38 ◽  
Author(s):  
K. V. Sokolovsky ◽  
Y. Y. Kovalev ◽  
A. B. Pushkarev ◽  
A. P. Lobanov
Keyword(s):  
The Core ◽  
Shift Effect ◽  
Core Shift

scholarly journals Jet kinematics of the quasar 4C+21.35 from observations with the KaVA very long baseline interferometry array

2019 ◽  
Vol 486 (2) ◽  
pp. 2412-2421 ◽  
Author(s):  
Taeseok Lee ◽  
Sascha Trippe ◽  
Motoki Kino ◽  
Bong Won Sohn ◽  
Jongho Park ◽  
...  
Keyword(s):  
Very Long Baseline Interferometry ◽  
Galactic Nuclei ◽  
Lorentz Factor ◽  
Time Resolved ◽  
The Core ◽  
Long Baseline ◽  
Boston University ◽  
Time Period ◽  
Spectrum Radio ◽  
Very Long Baseline Array

Abstract We present the jet kinematics of the flat spectrum radio quasar (FSRQ) 4C+21.35 using time-resolved KaVA very long baseline interferometry array radio maps obtained from 2014 September to 2016 July. During two out of three observing campaigns, observations were performed bi-weekly at 22 and 43 GHz quasi-simultaneously. At 22 GHz, we identified three jet components near the core with apparent speeds up to (14.4 ± 2.1)c. The timing of the ejection of a new component detected in 2016 is consistent with a γ-ray flare in 2014 November. At 43 GHz, we found four inner jet (<3 mas) components with speeds from (3.5 ± 1.4)c to (6.8 ± 1.5)c. Jet component speeds tend to be higher with increasing distances from the core. We compared our data with archival Very Long Baseline Array (VLBA) data from the Boston University (BU) 43 GHz and the Monitoring Of Jets in Active galactic nuclei with VLBA Experiments (MOJAVE) 15.4 GHz monitoring programmes. Whereas MOJAVE data and our data are in good agreement, jet speeds obtained from the BU programme data in the same time period are about twice as high as the ones we obtain from the KaVA data. The discrepancy at 43 GHz indicates that radio arrays with different angular resolution identify and trace different jet features even when the data are obtained at the same frequency and at the same time. The flux densities of jet components decay exponentially, in agreement with a synchrotron cooling time-scale of ∼1 yr. Using known electron Lorentz factor values (∼9000), we estimate the magnetic field strength to be ∼1–3 $\mu$T. When adopting a jet viewing angle of 5°, the intrinsic jet speed is of order 0.99c.

scholarly journals Jet-torus connection in radio galaxies

2018 ◽  
Vol 609 ◽  
pp. A80 ◽  
Author(s):  
C. M. Fromm ◽  
M. Perucho ◽  
O. Porth ◽  
Z. Younsi ◽  
E. Ros ◽  
...  
Keyword(s):  
Thermal Emission ◽  
Ambient Medium ◽  
Galactic Nuclei ◽  
Radio Galaxies ◽  
Asymmetric Structures ◽  
Long Baseline ◽  
Volume Method ◽  
Index Maps ◽  
Thermal Absorption ◽  
Core Shift

Context. High resolution very long baseline interferometry observations of active galactic nuclei have revealed asymmetric structures in the jets of radio galaxies. These asymmetric structures may be due to internal asymmetries in the jets or they may be induced by the different conditions in the surrounding ambient medium, including the obscuring torus, or a combination of the two. Aims. In this paper we investigate the influence of the ambient medium, including the obscuring torus, on the observed properties of jets from radio galaxies. Methods. We performed special-relativistic hydrodynamic (SRHD) simulations of over-pressured and pressure-matched jets using the special-relativistic hydrodynamics code Ratpenat, which is based on a second-order accurate finite-volume method and an approximate Riemann solver. Using a newly developed radiative transfer code to compute the electromagnetic radiation, we modelled several jets embedded in various ambient medium and torus configurations and subsequently computed the non-thermal emission produced by the jet and thermal absorption from the torus. To better compare the emission simulations with observations we produced synthetic radio maps, taking into account the properties of the observatory. Results. The detailed analysis of our simulations shows that the observed properties such as core shift could be used to distinguish between over-pressured and pressure matched jets. In addition to the properties of the jets, insights into the extent and density of the obscuring torus can be obtained from analyses of the single-dish spectrum and spectral index maps.

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