Observational consequences of optical band milliarcsec-scale structure in active galactic nuclei discovered by Gaia

Petrov, Leonid; Kovalev, Y. Y.

doi:10.1093/mnras/stx1747

Cited by 46 publications

(40 citation statements)

References 61 publications

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“…The height of the peak with respect to the background is 2.8 versus 1.7 and the full width at half maximum (FWHM) is 0.42 rad versus 0.62 rad. We confirmed that anisotropy of ψ angle is not an artifact of Gaia DR1, and the prediction made in Petrov & Kovalev (2017b) has come true.…”

Section: Analysis Of Vlbi/gaia Position Angles With Respect To the Jesupporting

confidence: 79%

“…Brightening a jet component shifts the centroid temporarily and irregularly. We call this behavior jitter and we predicted it in Petrov & Kovalev (2017b). Unlike to proper motions of stars, extending the observation interval does not result in a convergence of a proper motion estimate to some value with small uncertainty.…”

Section: Analysis Of Gaia and Vlbi Proper Motionsmentioning

confidence: 81%

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A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

Petrov

Kovalev

Plavin

2018

Monthly Notices of the Royal Astronomical Society

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We have analyzed the differences in positions of 9081 matched sources between the Gaia DR2 and VLBI catalogues. The median position uncertainty of matched sources in the VLBI catalogue is a factor of two larger than the median position uncertainty in the Gaia DR2. There are 9% matched sources with statistically significant offsets between both catalogues. We found that reported positional errors should be re-scaled by a factor of 1.3 for VLBI and 1.06 for Gaia, and in addition, Gaia errors should be multiplied by the square root of chi square per degree of freedom in order to best fit the normalized position differences to the Rayleigh distribution. We have established that the major contributor to statistically significant position offsets is the presence of optical jets. Among the sources for which the jet direction was determined, the position offsets are parallel to the jet directions for 62% of the outliers. Among the matched sources with significant proper motion, the fraction of objects with proper motion directions parallel to jets is a factor of 3 greater than on average. Such sources have systematically higher chi square per degree of freedom. We explain these proper motions as a manifestation of the source position jitter caused by flares that we have predicted earlier. Therefore, the assumption that quasars are fixed points and therefore, differential proper motions determined with respect to quasar photocenters can be regarded as absolute proper motions, should be treated with a great caution.

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Section: Analysis Of Vlbi/gaia Position Angles With Respect To the Jesupporting

confidence: 79%

Section: Analysis Of Gaia and Vlbi Proper Motionsmentioning

confidence: 81%

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

Petrov

Kovalev

Plavin

2018

Monthly Notices of the Royal Astronomical Society

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“…They also found that in 80% of Seyfert 2 galaxies, the associated Gaia position related to the jet is located farther away from the nucleus than the VLBI core. This offset could be explained by the presence of a bright extended optical jet which shifts the Gaia centroid [40,41]. While this interpretation might seem appealing in view of the extended lobe structure reported by Lal & Ho [11], in our VLBI data, we do not find any supporting evidence for large scale-jets, which makes this interpretation less likely.…”

Section: Vlbi Structure Of the Target Sourcescontrasting

confidence: 76%

High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars

et al. 2020

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Many low-luminosity active galactic nuclei (AGNs) contain a compact radio core which can be observed with high angular resolution using very long baseline interferometry (VLBI).Combining arcsec-scale structural information with milliarcsec-resolution VLBI imaging is a useful way to characterise the objects and to find compact cores on parsec scales. VLBI imaging could also be employed to look for dual AGNs when the sources show kpc-scale double symmetric structure with flat or inverted radio spectra. We observed five such sources at redshifts 0.36 < z < 0.58 taken from an optically selected sample of Type 2 quasars with the European VLBI Network (EVN) at 1.7 and 5 GHz. Out of the five sources, only one (SDSS J1026-0042) shows a confidently detected compact VLBI core at both frequencies. The other four sources are marginally detected at 1.7 GHz only, indicating resolved-out radio structure and steep spectra. Using first-epoch data from the ongoing Karl G. Jansky Very Large Array Sky Survey, we confirm that indeed all four of these sources have steep radio spectra on arcsec scale, contrary to the inverted spectra reported earlier in the literature. However, the VLBI-detected source, SDSS J1026−0042, has a flat integrated spectrum. Radio AGNs that show kpc-scale symmetric structures with truly flat or inverted spectra could still be promising candidates of dual AGNs, to be targeted with VLBI observations in the future.Symmetry 2020, xx, 1 2 of 14 low accretion rates (< 10 −2 − 10 −3 times the Eddington rate [3]). LLAGNs also have radio emission that seems originating from compact jets on parsec (pc) scales [3][4][5].Using the technique of very long baseline interferometry (VLBI), we can directly observe compact pc or even sub-pc scale radio emission. The baselines of the globally distributed radio telescope arrays, such as the European VLBI Network (EVN), are up to a few thousand kilometers long, providing milliarcsec (mas) or sub-mas resolution, depending on the observing frequency. Because of the high resolution, a VLBI detection of a radio source at GHz frequencies typically implies high brightness temperatures (T b > 10 6−7 K) that can be produced by the non-thermal (synchrotron) emission of AGNs [6,7]. A radio power exceeding 10 21 W Hz −1 in a source unresolved by the Karl G. Jansky Very Large Array (VLA) on arcsec scales is already indicative of accretion-powered nuclear activity [7] or maybe circumnuclear starburst. Detection of a compact core with VLBI in a high-luminosity source is a very strong AGN indicator.In LLAGNs, compact radio emission with flat (i.e., with spectral index −0.5 ≤ α ≤ 0, where the flux density is S ∝ ν α , and ν is the frequency) or inverted (α > 0) radio continuum spectrum can indicate radio emission that is fueled by a synchrotron self-absorbed jet base coupled to an underluminous accretion disk (e.g., [4]) or an accretion inflow onto the black hole [8]. When observed at high frequencies, magnetized plasma in the accretion disc corona can also produce compact sub-pc scale optically ...

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“…The smaller the viewing angle of a jet, the stronger is the Doppler boosting of the source emission leading to a "favoritism" in the observed properties of a flux limited AGN sample. Recent high-resolution observations of the jets in M 87 and 1H 0323+342 indicate the collimation and acceleration of the jets on scales up to hundreds of parsecs (Asada & Nakamura 2012, Hada et al 2017, Petrov & Kovalev 2017b.…”

Section: Introductionmentioning

confidence: 97%

Opacity, variability, and kinematics of AGN jets

Kutkin

Pashchenko

Sokolovsky

et al. 2019

Monthly Notices of the Royal Astronomical Society

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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 ∝ R 0.52±0.03 on de-projected scales R of 0.5-500 parsecs.

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Observational consequences of optical band milliarcsec-scale structure in active galactic nuclei discovered by Gaia

Cited by 46 publications

References 61 publications

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

High-Resolution Radio Observations of Five Optically Selected Type 2 Quasars

Opacity, variability, and kinematics of AGN jets

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