Opacity, variability, and kinematics of AGN jets

Kutkin, A. M.; Pashchenko, I. N.; Sokolovsky, K. V.; Kovalev, Y. Y.; Aller, M. F.; Aller, H. D.

doi:10.1093/mnras/stz885

Cited by 10 publications

(7 citation statements)

References 67 publications

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“…To address this problem, we could estimate the distance between the regions of the radio and gamma-ray emission production, taking the radio core opacity as the main source of the time lag (e.g. Kutkin et al 2019 ).…”

Section: Radio/gamma-ray Delay and Core Opacitymentioning

confidence: 99%

A decade of joint MOJAVE–Fermi AGN monitoring: localization of the gamma-ray emission region

Kramarenko

Pushkarev

Kovalev

et al. 2021

Monthly Notices of the Royal Astronomical Society

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Within the MOJAVE VLBA program (Monitoring of Jets in AGN with VLBA Experiments), we have accumulated observational data at 15 GHz for hundreds of jets in γ-ray bright active galactic nuclei since the beginning of the Fermi scientific observations in August 2008. We investigated a time delay between the flux density of AGN parsec-scale radio emission at 15 GHz and 0.1–300 GeV Fermi LAT photon flux, taken from constructed light curves using weekly and adaptive binning. The correlation analysis shows that radio is lagging γ-ray radiation by up to 8 months in the observer’s frame, while in the source frame, the typical delay is about 2-3 months. If the jet radio emission, excluding the opaque core, is considered, significant correlation is found at greater time lags. We supplement these results with VLBI kinematics and core shift data to conclude that the dominant high-energy production zone is typically located at a distance of several parsecs from the central nucleus. We also found that quasars have on average more significant correlation peak, more distant γ-ray emission region from the central engine and shorter variability time scale compared to those of BL Lacertae objects.

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Section: Radio/gamma-ray Delay and Core Opacitymentioning

confidence: 99%

A decade of joint MOJAVE–Fermi AGN monitoring: localization of the gamma-ray emission region

Kramarenko

Pushkarev

Kovalev

et al. 2021

Monthly Notices of the Royal Astronomical Society

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“…We estimate the component speed from the apparent speed of the jet features β app . Kutkin et al [32] showed that the jet speed, which is found by time delay of a flare when the observed frequency decreases, corresponds to the maximum β app estimated from the apparent motion of jet components. Therefore, we used the maximum value of β app = 15.31 for OJ 287 [33] to find β = 0.9979 assuming Γ min = (1 + β 2 app ) 1/2 .…”

Section: Connection Between Long-term Optical and Radio Flux Variabilitymentioning

confidence: 99%

Is OJ 287 a Single Supermassive Black Hole?

Butuzova

Pushkarev

2020

Universe

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Light curves for more than century optical photometric observations of the blazar OJ 287 reveals strong flares with a quasi-period of about 12 years. For a long time, this period has been interpreted by processes in a binary black hole system. We propose an alternative explanation for this period, which is based on Doppler factor periodic variations of the emitting region caused by jet helicity. Using multi-epoch very large baseline interferometry (VLBI) observations carried out in a framework of the MOJAVE (Monitoring Of Jets in Active galactic nuclei with VLBA Experiments) program and other VLBA (Very Long Baseline Array) archival experiments at the observing frequency of 15 GHz, we derived geometrical parameters of the jet helix. To reach an agreement between the VLBI and photometric optical observation data, the jet component motion at a small angle to the radial direction is necessary. Such non-radial motion is observed and, together with the jet helical shape, can be naturally explained by the development of the Kelvin–Helmholtz instability in the parsec-scale outflow. In this case, the true precession of the OJ 287 jet may manifest itself in differences between the peak flux values of the 12-year optical flares. A possibility to create this precession due to Lense–Thirring effect of a single supermassive black hole is also discussed.

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“…If a source demonstrates flaring activity, it is possible to derive the kinematics of the jet innermost regions based on the measured core shift and multi-frequency time delays (Kudryavtseva et al 2011;Kutkin et al 2014Kutkin et al , 2018Kutkin et al , 2019. Assuming that the peak of a flare at a given frequency is observed when a moving jet feature passes through the region of the core at that frequency, it is possible to estimate the apparent projected speed of the component by comparing the light curve time delay, 𝑡, with the core shift for a pair of frequencies, 𝑟: 𝜇 app = 𝑟 / 𝑡.…”

Section: Agn Jets: Flares Speeds and Geometrymentioning

confidence: 99%

“…They were also used to constrain the spins of the supermassive black holes (Agarwal et al 2017) and the nature of the central engine (Zamaninasab et al 2014). If a source demonstrates flaring activity, it is possible to derive the jets innermost regions kinematics based on the measured core shift and multi-frequency time delays (Kudryavtseva et al 2011;Kutkin et al 2014Kutkin et al , 2018Kutkin et al , 2019Plavin et al 2019a). Differences in core positions should be taken into account for image registration when constructing the VLBI spectral index (e.g.…”

Section: Introductionmentioning

confidence: 99%

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

Pashchenko,

Plavin,

Kutkin

et al. 2020

Preprint

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The Blandford and Königl model of 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 two 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.

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Opacity, variability, and kinematics of AGN jets

Cited by 10 publications

References 67 publications

A decade of joint MOJAVE–Fermi AGN monitoring: localization of the gamma-ray emission region

A decade of joint MOJAVE–Fermi AGN monitoring: localization of the gamma-ray emission region

Is OJ 287 a Single Supermassive Black Hole?

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

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