Testing the magnetic flux paradigm for AGN radio loudness with a radio-intermediate quasar

Chamani, Wara; Savolainen, Tuomas; Hada, Kazuhiro; Mei-ling, XU

doi:10.1051/0004-6361/202140676

Cited by 12 publications

(15 citation statements)

References 84 publications

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“…One possibility is that the central engines in high-redshift AGNs have not yet reached the magnetically arrested disk (MAD) state (Narayan et al 2003). A similar case can be seen in the nearby radio-intermediate quasar III Zw 2 (Chamani et al 2021). Measurements of the magnetic field strength in high-z jets and high-resolution numerical simulations would help to solve this puzzle.…”

Section: Resultsmentioning

confidence: 62%

VLBI observations of VIK J2318−3113, a quasar at z = 6.44

Zhang

Wang

et al. 2022

A&A

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Context. The nature of jets in active galactic nuclei (AGNs) in the early Universe and their feedback to the host galaxy remains a highly topical question. Observations of the radio structure of high-redshift AGNs enabled by very long baseline interferometry (VLBI) provide indispensable input into studies of their properties and role in the galaxies’ evolution. To date, only five AGNs at redshift z > 6 have been studied with the VLBI technique. Aims. VIK J2318−3113 is a recently discovered quasar at z = 6.44 that had not been imaged with VLBI before the current work. Here we present the first VLBI imaging results of this high-redshift quasar, with the aim of corroborating its high-resolution appearance with the physical model of the object. Methods. We carried out VLBI phase-referencing observations of VIK J2318−3113 using the Very Long Baseline Array at two frequencies, 1.6 and 4.7 GHz, and obtained the first view at the radio structure on the milliarcsecond scale. Results. The source was clearly detected at 1.6 GHz. We found that almost all of its radio emission comes from the parsec-scale core region. Our dual-frequency observations constrain the spectral index and brightness temperature of the radio core. Its properties are similar to those of other known high-redshift radio-loud AGNs.

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Section: Resultsmentioning

confidence: 62%

VLBI observations of VIK J2318−3113, a quasar at z = 6.44

Zhang

Wang

et al. 2022

A&A

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“…The 2D crosscorrelation technique has been widely used to align multifrequency VLBI images (e.g. Walker et al 2000;Kovalev et al 2008;Croke & Gabuzda 2008;O'Sullivan & Gabuzda 2009;Hovatta et al 2012;Pushkarev et al 2012;Kutkin et al 2014;Kravchenko et al 2016;PL19;Chamani et al 2021).…”

Section: D Cross-correlation Of the Imagesmentioning

confidence: 99%

“…Several studies have confirmed r core ∝ ν −1 obs (Lobanov 1998;Hirotani 2005;O'Sullivan & Gabuzda 2009;Fromm et al 2010Fromm et al , 2013bFromm et al , 2015Sokolovsky et al 2011;Hada et al 2011;Mohan et al 2015;Lisakov et al 2017;Pushkarev et al 2018) and the amount of core shift together with the equipartition assumption has been frequently used to infer jet magnetic field strengths (e.g. Pushkarev et al 2012;Voitsik et al 2018;Plavin et al 2019b, hereafter PL19;Chamani et al 2021). However, there is very little knowledge of the stability of the index k r over time or how this affects the inferred magnetic field strength.…”

Section: Introductionmentioning

confidence: 99%

Time variability of the core-shift effect in the blazar 3C 454.3

Chamani¹,

Savolainen²

2023

A&A

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Measuring and inferring the key physical parameters of jets in active galactic nuclei (AGN) requires high-resolution very long baseline interferometry (VLBI) observations. Using VLBI to measure a core-shift effect is a common way of obtaining estimates of the jet magnetic field strength, a key parameter for understanding jet physics. The VLBI core is typically identified as the bright feature at the upstream end of the jet, and the position of this feature changes with the observed frequency, rcore ∝ ν−1/kr. Due to the variable nature of AGN, flares can cause variability of the measured core shift. In this work, we investigated the time variability of the core-shift effect in the luminous blazar 3C 454.3. We employed a self-referencing analysis of multi-frequency (5, 8, 15, 22−24, and 43 GHz) Very Long Baseline Array (VLBA) data covering 19 epochs from 2005 to 2010. We found significant core-shift variability ranging from 0.27 to 0.86 milliarcsec between 5 GHz and 43 GHz. These results confirm the core-shift variability phenomenon observed previously. Furthermore, we also found time variability of the core-shift index, kr, which was typically below one, with an average value of 0.85 ± 0.08 and a standard deviation of 0.30. Values of kr below one were found during flaring and quiescent states. Our results indicate that the commonly assumed conical jet shape and equipartition conditions do not always hold simultaneously. Even so, these conditions are typically assumed when deriving magnetic field strengths from core-shift measurements, which can lead to unreliable results if kr significantly deviates from unity. Therefore, it is necessary to verify that kr = 1 actually holds before using core-shift measurements and the equipartition assumption to derive physical conditions in the jets. When kr = 1 epochs are selected in the case of 3C 454.3, the magnetic field estimates are consistent, even though the core shift varies significantly with time. Subsequently, we estimated the magnetic flux in the jet of 3C 454.3 and found that the source is in the magnetically arrested disc state, which agrees with earlier studies. Finally, we found a good correlation of the core position with the core flux density, rcore ∝ Score0.7, which is consistent with increased particle density during the flares.

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“…Significant simplifications were adopted to obtain these results and a detailed critical discussion was presented by Gralla (Gralla, 2021). On a more general point of view, it is worth citing the Very Long Baseline Array (VLBA) study on III Zw 2 (z 0.089 8), a c-ray intermediate Seyfert (Liao et al, 2016), which revealed that the measured magnetic field in the innermost region was well below the value prescribed by the MAD model (Chamani et al, 2021). III Zw 2 has an accretion rate greater than M87 [∼ 0.04 vs. ∼ 2 × 10 −5 (Berton et al, 2015;Akiyama et al, 2019e)], which implies a likely different accretion disk, much more radiatively efficient.…”

Section: High-resolution Radio Observationsmentioning

confidence: 99%

Some Notes About the Current Researches on the Physics of Relativistic Jets

Foschini

2022

Front. Astron. Space Sci.

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Some highlights of the recent researches in the field of relativistic jets are reviewed and critically analyzed. Given the extent of the available literature, this essay symbolically takes the baton from the outstanding and recent review by Blandford, Meier, and Readhead (2019). Therefore, I focus mostly on the results published during the latest few years, with specific reference to jets from active galactic nuclei.

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Testing the magnetic flux paradigm for AGN radio loudness with a radio-intermediate quasar

Cited by 12 publications

References 84 publications

VLBI observations of VIK J2318−3113, a quasar at z = 6.44

VLBI observations of VIK J2318−3113, a quasar at z = 6.44

Time variability of the core-shift effect in the blazar 3C 454.3

Some Notes About the Current Researches on the Physics of Relativistic Jets

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