On the estimation of a celestial reference frame in the presence of source structure

Plank, Lucia; Shabala, Stanislav S.; McCallum, Jamie; Krásná, Hana; Petrachenko, Bill; Rastorgueva-Foi, Elizaveta; Lovell, J. E. J.

doi:10.1093/mnras/stv2080

Cited by 10 publications

(8 citation statements)

References 28 publications

(40 reference statements)

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“…This guarantees that, for a given observation, the relative angle between the observing baseline and source structure direction (i.e., the quasar jet projected in the plane of the sky) remains fixed from day to day. As a consequence, we expected the systematic effects of quasar source structure (e.g., Shabala et al 2015;Plank et al 2016) to be the same each day and, hence, to not affect repeatabilities of results during one campaign. For A13, we went even further, repeating two different schedules: one with only good sources (or a nominal structure index (SI, Fey and Charlot 1997;Ma et al 2009) smaller than 2.5) and a second schedule with only bad sources with SI higher than 2.5.…”

Section: Weekend and Aust-cont Experimentsmentioning

confidence: 99%

The AUSTRAL VLBI observing program

Plank

Lovell

McCallum

et al. 2016

J Geod

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The AUSTRAL observing program was started in 2011, performing geodetic and astrometric very long baseline interferometry (VLBI) sessions using the new Australian AuScope VLBI antennas at Hobart, Katherine, and Yarragadee, with contribution from the Warkworth (New Zealand) 12 m and Hartebeesthoek (South Africa) 15 m antennas to make a southern hemisphere array of telescopes with similar design and capability. Designed in the style of the nextgeneration VLBI system, these small and fast antennas allow for a new way of observing, comprising higher data rates and more observations than the standard observing sessions coordinated by the International VLBI Service for Geodesy and Astrometry (IVS). In this contribution, the continuous development of the AUSTRAL sessions is described, leading to an improvement of the results in terms of baseline length repeatabilities by a factor of two since the start of this program. The focus is on the scheduling strategy and increased number of observations, aspects of automated operation, and data logistics, as well as results of the 151 AUSTRAL sessions performed so far. The high number of the AUSTRAL

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Section: Weekend and Aust-cont Experimentsmentioning

confidence: 99%

The AUSTRAL VLBI observing program

Plank

Lovell

McCallum

et al. 2016

J Geod

Self Cite

View full text Add to dashboard Cite

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“…The effects of the source structure and its frequency dependence on these positions were extensively studied: see, e.g. Porcas (2009), Plank et al (2016), Xu et al (2017), Anderson & Xu (2018). Single-band measurements are sensitive to the brightest part position itself; thus, they are affected by the full magnitude of the core position bias addressed in this paper.…”

Section: Astrometric Implicationsmentioning

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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“…There are several possibilities that make radio sources apparently unstable. The main origin is the temporal evolution of the radio source structure due to intrinsic variability such as the ejection of new jet features, which could manifest itself as an apparent proper motion (Fomalont et al 2011;Moór et al 2011) or positional offset along the jet (Plank et al 2016). Other causes include the difference in radio source position as "seen" by different VLBI networks (Dehant et al 2003) and the weak mi-A&A proofs: manuscript no.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the ICRF stability from position time series analysis

Liu,

Lambert,

Arias

et al. 2021

Preprint

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Context. The celestial reference frame is realized by absolute positions of extragalactic sources that are assumed to be fixed in the space. The fixing of the axes is one of the crucial points for the International Celestial Reference System (ICRS) concept. However, due to various effects such as its intrinsic activity, the apparent position of the extragalactic sources may vary with time, resulting in a time-dependent deviation of the frame axes that are defined by the positions of these sources. Aims. We aim to evaluate the axis stability of the third realization of the International Celestial Reference Frame (ICRF3). Methods. We first derive the extragalactic source position time series from observations of very long baseline interferometry (VLBI) at the dual S /X-band (2.3/8.4 GHz) between August 1979 and December 2020. We measure the stability of the ICRF3 axes in terms of the drift and scatter around the mean: (i) we estimate the global spin of the ICRF3 axes based on the apparent proper motion (slope of the position time series) of the ICRF3 defining sources; (ii) we also construct the yearly representations of the ICRF3 through annually averaged positions of the ICRF3 defining sources and estimate the dispersion in the axis orientation of these yearly frames. Results. The global spin is no higher than 0.8 µas yr −1 for each ICRF3 axis with an uncertainty of 0.3 µas yr −1 , corresponding to an accumulated deformation smaller than 30 µas for the celestial frame axes during 1979.6-2021.0. The axes orientation of the yearly celestial frame becomes more stable as time elapses, with a standard deviation of 10-20 µas for each axis. Conclusions. The axes of the ICRF3 are stable at approximately 10-20 µas from 1979.6-2021.0 and the axis stability does not degrade after the adoption of the ICRF3.

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On the estimation of a celestial reference frame in the presence of source structure

Cited by 10 publications

References 28 publications

The AUSTRAL VLBI observing program

The AUSTRAL VLBI observing program

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

Evaluation of the ICRF stability from position time series analysis

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