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

Chamani, Wara; Savolainen, Tuomas

doi:10.1051/0004-6361/202243435

“…However, k r measured in 2020 shows a larger deviation. The value of k r (lower than 1) and its change with time is very similar to the blazar 3C 454.3 studied by Chamani et al (2023), with wide multifrequency and multiepoch observations, who found the value of k r for 3C 454.3 varies between ∼1 and values lower than 1.…”

Section: | = Dsupporting

confidence: 80%

“…for a given frequency pair) and OS is the difference of the core coordinates. The corresponding uncertainties were derived by using the method described in the study of Chamani et al (2021Chamani et al ( , 2023. In our study, the uncertainty of the core shift is estimated as…”

Section: | = Dmentioning

confidence: 99%

Evolution of Magnetic Field of the Quasar 1604+159 at parsec Scale

Hu,

Hong,

Zhao

et al. 2024

ApJ

1

0

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We have analyzed the total intensity, spectral index, linear polarization, and rotation measure (RM) distributions at the parsec scale for the quasar 1604+159. The source was observed at 5.0, 8.4, and 15.4 GHz in 2002 and 4.6, 5.1, 6.0, 7.8, 12.2, 15.2, and 43.9 GHz in 2020 with the American Very Long Baseline Array (VLBA). Combining the polarization results of Monitoring of Jets in Active Galactic Nuclei with VLBA Experiments at 15 GHz from 2009 to 2013, we studied the evolution of magnetic field at the parsec scale for the source. We detected a core-jet structure. The jet extends to the distance of ∼25 mas from the core at a direction of ∼66° north by east. The shape of the jet derived from 15 GHz data varies slightly with time and could be described by a straight line. Based on the linear polarization distribution in 2002, we divided the source structure into the central region and the jet region. In the jet region, we find the polarized emission varies with time. The flatter spectral index values and electric vector position angle direction indicate the possible existence of shocks, contributing to the variation of polarization in the jet with time. In the central region, the derived core shift index k r values indicate that the core in 2002 is close to the equipartition case, while it deviated from the case in 2020. The measured magnetic field strength in 2020 is 2 orders of magnitude lower than that in 2002. We detected transverse RM gradients, evidence of a helical magnetic field, in the core. The polarized emission orients in general toward the jet direction in the core. At 15 GHz, in the place close to the jet base, the polarization direction changes significantly with time from perpendicular to parallel to the jet direction. The evolution of RM and magnetic field structure are potential reasons for the observed polarization change. The core ∣RM∣ in 2020 increases with frequency following a power law with index a = 2.7 ± 0.5, suggesting a fast electron density falloff in the medium with distance from the jet base.

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“…pattern (Sokolovsky et al 2011;Chamani et al 2023). In our VLBA observations, the C1 component at 5.5 and 8.5 GHz is core dominated.…”

Section: A Parsec-scale Jet or An Outflow?supporting

confidence: 45%

A Large Jet Narrow-line Seyfert 1 Galaxy: Observations from Parsec to 100 kpc Scales

Chen,

Kharb,

Sasikumar

et al. 2024

ApJ

1

0

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We present new 1.5–8.5 GHz Very Long Baseline Array (VLBA) observations and 0.32–1.26 GHz Giant Meterwave Radio Telescope (GMRT) observations of J0354−1340, which is the only known radio-quiet (RQ) or radio-intermediate (RI) narrow-line Seyfert 1 galaxy with a 100 kpc, two-sided radio jet. A parsec-scale, one-sided jet in the southeastern direction from the core emission is found in the VLBA observations, while the kiloparsec-scale jet observed with the Karl G. Jansky Very Large Array (VLA) and GMRT is in the south–north direction. Core spectra on parsec and kiloparsec scales are presented in combination with archival VLA Sky Survey observations at 3.0 GHz and VLA C-configuration observations at 5.5 GHz. The parsec-scale emission dominates the kiloparsec-scale emission above ∼5 GHz, and the spectrum is inverted due to synchrotron self-absorption. This indicates a compact synchrotron source with a size of ∼0.04 pc, which is associated with either the jet base or the corona. A subkiloparsec-scale jet, which is unresolved on scales of ∼3″, probably dominates the emission below ∼5 GHz. Future radio observations can explore the jet structure between the parsec and 100 kpc scales, the origin of their direction mismatch, and the parsec-scale jet proper motion. It remains to be explored how common such large-scale jets are in RQ or RI active galactic nuclei.

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“…From the physical point of view, the high T B,int , especially close to the inverse-Compton limit, can be due to an increased number of energetic and emitting electrons, for instance due to strong particle acceleration by turbulence (e.g., Marscher 2014) or other mechanisms (see discussions in Kovalev et al 2016). The changing particle density can also cause significant variations in the nuclear opacity, as observed by time-variable shift of the VLBI core positions (Plavin et al 2019;Chamani et al 2023). We note that the arcsecond-scale core of M87 shows elevated X-ray flux density around 2014 (Sun et al 2018), which could be supporting evidence for higher T B,int in 2014 February than other epochs.…”

Section: Discussionmentioning

confidence: 99%

RadioAstron Space VLBI Imaging of the Jet in M87. I. Detection of High Brightness Temperature at 22 GHz

Kim

¹

,

Savolainen

²

,

Voitsik

³

et al. 2023

ApJ

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We present results from the first 22 GHz space very long baseline interferometric (VLBI) imaging observations of M87 by RadioAstron. As a part of the Nearby AGN Key Science Program, the source was observed in 2014 February at 22 GHz with 21 ground stations, reaching projected (u, v) spacings up to ∼11 Gλ. The imaging experiment was complemented by snapshot RadioAstron data of M87 obtained during 2013–2016 from the AGN Survey Key Science Program. Their longest baselines extend up to ∼25 Gλ. For all of these measurements, fringes are detected only up to ∼2.8 Earth diameter or ∼3 Gλ baseline lengths, resulting in a new image with angular resolution of ∼150 μas or ∼20 Schwarzschild radii spatial resolution. The new image not only shows edge-brightened jet and counterjet structures down to submilliarcsecond scales but also clearly resolves the VLBI core region. While the overall size of the core is comparable to those reported in the literature, the ground-space fringe detection and slightly superresolved RadioAstron image suggest the presence of substructures in the nucleus, whose minimum brightness temperature exceeds T B , min ∼ 10 12 K. It is challenging to explain the origin of this record-high T B , min value for M87 by pure Doppler boosting effect with a simple conical jet geometry and known jet speed. Therefore, this can be evidence for more extreme Doppler boosting due to a blazar-like small jet viewing angle or highly efficient particle acceleration processes occurring already at the base of the outflow.

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

Cited by 8 publications

References 94 publications

Evolution of Magnetic Field of the Quasar 1604+159 at parsec Scale

Evolution of Magnetic Field of the Quasar 1604+159 at parsec Scale

A Large Jet Narrow-line Seyfert 1 Galaxy: Observations from Parsec to 100 kpc Scales

RadioAstron Space VLBI Imaging of the Jet in M87. I. Detection of High Brightness Temperature at 22 GHz

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