Polarization Observations of AGN Jets: Past and Future

Park, Jong Ho; Algaba, Juan Carlos

doi:10.3390/galaxies10050102

Cited by 8 publications

(2 citation statements)

References 161 publications

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“…Recent studies on a large sample of AGN have shown a tendency for EVPAs to be aligned with the jet in BL Lac objects, with quasars having less of that tendency ( [12]). In addition, temporal changes in the EVPAs over time have been observed at both radio and optical wavelengths, as well as tight correlations between the two bands (see, e.g., [13] for a review). EVPAs parallel (i.e., for the optically thin case, 𝐵-field orthogonal) to the jet are expected for plane shock waves, where the 𝐵-field is compressed along the jet.…”

Section: Magnetic Fields In Agn Jetsmentioning

confidence: 94%

Rotation Measure studies of the quasar 3C 345 with RadioAstron

Poetzl¹

2023

Proceedings of 15th European VLBI Network Mini-Symposium and Users' Meeting — PoS(EVN2022)

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A fraction of about 10 % of supermassive black holes in the centres of active galactic nuclei (AGN) produce powerful jets emitting across the electromagnetic spectrum. The formation of jets and what collimates them on parsec scales is still poorly understood and debated to date. Many jet launching scenarios predict the existence of helical magnetic fields in the jet, potentially being one of the jet collimation mechanisms and manifesting themselves in polarisation structure and transverse Faraday rotation gradients. Therefore, studying the magnetic fields on the smallest possible scales in AGN jets can give crucial insight into the physics of jet launching, acceleration and collimation. This is one of the main aims of the RadioAstron mission, which operated from 2011 to 2019. The 10-m antenna onboard the Spektr-R spacecraft in a highly elliptical orbit with major axis of 350,000 km was complemented by a ground-array of telescopes, including the EVN, at observing frequencies of 0.32, 1.6, and 22 GHz with full polarisation capabilities. The powerful flat-spectrum radio quasar (FSRQ) 3C 345 is one of those archetypical AGN that underwent several flaring episodes in the optical, 𝛾-rays and at radio wavelengths. Observed with VLBI over several decades, it shows a compact jet closely aligned with the line of sight, with components exhibiting apparent superluminal motion. We observed 3C 345 with RadioAstron at 1.6 GHz on March 30, 2016, resulting in the highestresolution image of this source at this frequency to date (see [1]) with a resolution along the jet direction of ∼300 𝜇as. In addition to the published results we present studies of the spectral index and the rotation measure in the source. These were obtained with the RadioAstron data in conjunction with ground-VLBI data from the same epoch. We test for possible Faraday rotation gradients and study the change of the electric vector position angles.

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Section: Magnetic Fields In Agn Jetsmentioning

confidence: 94%

Rotation Measure studies of the quasar 3C 345 with RadioAstron

Poetzl¹

2023

Proceedings of 15th European VLBI Network Mini-Symposium and Users' Meeting — PoS(EVN2022)

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“…2 Other calibration/imaging pipelines that have recently been developed are polsolve (Martí-Vidal et al 2021), similar to GP-CAL but based on CASA (Janssen et al 2019;THE CASA TEAM et al 2022;van Bemmel et al 2022), the eht-imaging software library using the regularized maximum likelihood technique (Chael et al 2016(Chael et al , 2018(Chael et al , 2022, D-term Modeling Code (DMC, Pesce 2021), THEMIS (Broderick et al 2020), and Comrade (Tiede 2022) using Markov chain Monte Carlo schemes. See Park & Algaba (2022) for more details.…”

Section: Introductionmentioning

confidence: 99%

GPCAL: A Generalized Calibration Pipeline for Instrumental Polarization in VLBI Data

Park

Byun

Asada

et al. 2021

ApJ

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In this series of papers, we present new methods of frequency-and time-dependent instrumental polarization calibration for Very Long Baseline Interferometry (VLBI). In most existing calibration tools and pipelines, it has been assumed that instrumental polarization is constant over frequency within the instrument bandwidth and over time. The assumption is not always true and may prevent an accurate calibration, which can result in degradation of the quality of linear polarization images. In this paper, we present a method of frequency-dependent instrumental polarization calibration that is implemented in GPCAL, a recently developed polarization calibration pipeline. The method is tested using simulated data sets generated from real Very Long Baseline Array (VLBA) data. We present the results of appyling the method to real VLBA data sets observed at 15 and 43 GHz. We were able to eliminate significant variability in cross-hand visibilities over frequency that is caused by frequency-dependent instrumental polarization. As a result of the calibration, linear polarization images were slightly to modestly improved as compared to those obtained without frequency-dependent instrumental polarization calibration. We discuss the reason for the minor impact of frequency-dependent instrumental polarization calibration on existing VLBA data sets and prospects for applying the method to future VLBI data sets, which are expected to provide very large bandwidths.

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3D hybrid fluid-particle jet simulations and the importance of synchrotron radiative losses

Kramer,

MacDonald,

Paraschos

et al. 2024

A&A

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Context. Relativistic jets in active galactic nuclei are known for their exceptional energy output, and imaging the synthetic synchrotron emission of numerical jet simulations is essential for a comparison with observed jet polarization emission. Aims. Through the use of 3D hybrid fluid-particle jet simulations (with the PLUTO code), we overcome some of the commonly made assumptions in relativistic magnetohydrodynamic (RMHD) simulations by using non-thermal particle attributes to account for the resulting synchrotron radiation. Polarized radiative transfer and ray-tracing (via the RADMC-3D code) highlight the differences in total intensity maps when (i) the jet is simulated purely with the RMHD approach, (ii) a jet tracer is considered in the RMHD approach, and (iii) a hybrid fluid-particle approach is used. The resulting emission maps were compared to the example of the radio galaxy Centaurus A. Methods. We applied the Lagrangian particle module implemented in the latest version of the PLUTO code. This new module contains a state-of-the-art algorithm for modeling diffusive shock acceleration and for accounting for radiative losses in RMHD jet simulations. The module implements the physical postulates missing in RMHD jet simulations by accounting for a cooled ambient medium and strengthening the central jet emission. Results. We find a distinction between the innermost structure of the jet and the back-flowing material by mimicking the radio emission of the Seyfert II radio galaxy Centaurus A when considering an edge-brightened jet with an underlying purely toroidal magnetic field. We demonstrate the necessity of synchrotron cooling as well as the improvements gained when directly accounting for non-thermal synchrotron radiation via non-thermal particles.

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Polarization Observations of AGN Jets: Past and Future

Cited by 8 publications

References 161 publications

Rotation Measure studies of the quasar 3C 345 with RadioAstron

Rotation Measure studies of the quasar 3C 345 with RadioAstron

GPCAL: A Generalized Calibration Pipeline for Instrumental Polarization in VLBI Data

3D hybrid fluid-particle jet simulations and the importance of synchrotron radiative losses

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