Source structure: an essential piece of information for generating the next ICRF

AbstractThe intrinsic radio structure of the extragalactic sources is one of the limiting factors in defining the International Celestial Reference Frame (ICRF). This paper reports about the ongoing work to monitor the structural evolution of the ICRF sources by using the Very Long Baseline Array and other VLBI telescopes around the world. Based on more than 5000 VLBI images produced from such observations, we have assessed the astrometric suitability of 80% of the ICRF sources. The number of VLBI images for a given source varies from 1 for the least-observed sources to more than 20 for the intensively-observed sources. Overall, we identify a subset of 194 sources that are highly compact at any of the available epochs and which are prime candidates for the realization of the next ICRF with the highest accuracy.

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Models for Source Structure Corrections

International Astronomical Union Colloquium ◽

10.1017/s0252921100000075 ◽

2000 ◽

Vol 180 ◽

pp. 29-39

Author(s):

P. Charlot

Keyword(s):

Reference Frame ◽

Very Long Baseline Interferometry ◽

Radio Sources ◽

Time Varying ◽

Long Baseline ◽

Vlbi Observations ◽

Spatially Extended ◽

Astrometric Data ◽

Celestial Reference Frame ◽

Source Structure

AbstractAt the milliarcsecond scale, most of the extragalactic radio sources exhibit spatially-extended intrinsic structures which are variable in both time and frequency. Such radio structures set limits on the accuracy of source positions determined with the Very Long Baseline Interferometry (VLBI) technique unless their effects in the astrometric data can be accounted for. We review the modeling scheme for calculating source structure corrections and discuss the magnitude and impact of these effects for the sources that are part of the International Celestial Reference Frame (ICRF). Results obtained by applying source structure corrections to actual VLBI observations on the time-varying source 4C39.25 (0923 + 392) are also presented.

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The Celestial Frame and the Weighting of the Celestial Pole Offsets in the Computation of VLBI-Based Corrections for the Main Lunisolar Nutation Terms

Sensors ◽

10.3390/s21248276 ◽

2021 ◽

Vol 21 (24) ◽

pp. 8276

Author(s):

Víctor Puente ◽

Marta Folgueira

Keyword(s):

Stochastic Model ◽

Least Squares ◽

Reference Frame ◽

Very Long Baseline Interferometry ◽

Long Baseline ◽

Celestial Pole ◽

Two Factors ◽

Least Squares Adjustment ◽

Empirical Corrections ◽

Celestial Reference Frame

Very long baseline interferometry (VLBI) is the only technique in space geodesy that can determine directly the celestial pole offsets (CPO). In this paper, we make use of the CPO derived from global VLBI solutions to estimate empirical corrections to the main lunisolar nutation terms included in the IAU 2006/2000A precession–nutation model. In particular, we pay attention to two factors that affect the estimation of such corrections: the celestial reference frame used in the production of the global VLBI solutions and the stochastic model employed in the least-squares adjustment of the corrections. In both cases, we have found that the choice of these aspects has an effect of a few μas in the estimated corrections.

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

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stv2080 ◽

2015 ◽

Vol 455 (1) ◽

pp. 343-356 ◽

Cited By ~ 5

Author(s):

L. Plank ◽

S. S. Shabala ◽

J. N. McCallum ◽

H. Krásná ◽

B. Petrachenko ◽

...

Keyword(s):

Reference Frame ◽

Celestial Reference Frame ◽

Source Structure

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Variability and parsec-scale radio structure of candidate compact symmetric objects

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2856 ◽

2020 ◽

Vol 499 (1) ◽

pp. 1340-1355 ◽

Cited By ~ 1

Author(s):

M Orienti ◽

D Dallacasa

Keyword(s):

Flux Density ◽

Expansion Velocity ◽

Radio Structure ◽

Very Large Array ◽

Long Baseline ◽

Thick Part ◽

Thin Part ◽

Almost All ◽

Very Long Baseline Array ◽

Fast Evolution

ABSTRACT We report results on multiepoch Very Large Array (VLA) and pc-scale Very Long Baseline Array (VLBA) observations of candidate compact symmetric objects (CSOs) from the faint sample of high-frequency peakers. New VLBA observations could resolve the radio structure in about 42 per cent of the observed sources, showing double components that may be either mini-lobes or core-jet structures. Almost all the sources monitored by the VLA show some variability on time-scale of a decade, and only one source does not show any significant variation. In 17 sources, the flux density changes randomly as it is expected in blazars, and in four sources the spectrum becomes flat in the last observing epoch, confirming that samples selected in the GHz regime are highly contaminated by beamed objects. In 16 objects, the pc-scale and variability properties are consistent with a young radio source in adiabatic expansion, with a steady decrease of the flux density in the optically thin part of the spectrum, and a flux density increase in the optically thick part. For these sources, we estimate dynamical ages between a few tens to a few hundred years. The corresponding expansion velocity is generally between 0.1c and 0.7c, similar to values found in CSOs with different approaches. The fast evolution that we observe in some CSO candidates suggests that not all the objects would become classical Fanaroff–Riley radio sources.

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The International Celestial Reference Frame as Realized by Very Long Baseline Interferometry

The Astronomical Journal ◽

10.1086/300408 ◽

1998 ◽

Vol 116 (1) ◽

pp. 516-546 ◽

Cited By ~ 461

Author(s):

C. Ma ◽

E. F. Arias ◽

T. M. Eubanks ◽

A. L. Fey ◽

A.-M. Gontier ◽

...

Keyword(s):

Reference Frame ◽

Very Long Baseline Interferometry ◽

Long Baseline ◽

Celestial Reference Frame

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The third realization of the International Celestial Reference Frame by very long baseline interferometry

Astronomy and Astrophysics ◽

10.1051/0004-6361/202038368 ◽

2020 ◽

Vol 644 ◽

pp. A159 ◽

Cited By ~ 3

Author(s):

P. Charlot ◽

C. S. Jacobs ◽

D. Gordon ◽

S. Lambert ◽

A. de Witt ◽

...

Keyword(s):

Reference Frame ◽

Very Long Baseline Interferometry ◽

Galactic Center ◽

Motion Field ◽

Dual Frequency ◽

Extended Source ◽

Long Baseline ◽

Radio Frequencies ◽

Celestial Reference Frame ◽

24 Ghz

A new realization of the International Celestial Reference Frame (ICRF) is presented based on the work achieved by a working group of the International Astronomical Union (IAU) mandated for this purpose. This new realization follows the initial realization of the ICRF completed in 1997 and its successor, ICRF2, adopted as a replacement in 2009. The new frame, referred to as ICRF3, is based on nearly 40 years of data acquired by very long baseline interferometry at the standard geodetic and astrometric radio frequencies (8.4 and 2.3 GHz), supplemented with data collected at higher radio frequencies (24 GHz and dual-frequency 32 and 8.4 GHz) over the past 15 years. State-of-the-art astronomical and geophysical modeling has been used to analyze these data and derive source positions. The modeling integrates, for the first time, the effect of the galactocentric acceleration of the solar system (directly estimated from the data) which, if not considered, induces significant deformation of the frame due to the data span. The new frame includes positions at 8.4 GHz for 4536 extragalactic sources. Of these, 303 sources, uniformly distributed on the sky, are identified as “defining sources” and as such serve to define the axes of the frame. Positions at 8.4 GHz are supplemented with positions at 24 GHz for 824 sources and at 32 GHz for 678 sources. In all, ICRF3 comprises 4588 sources, with three-frequency positions available for 600 of these. Source positions have been determined independently at each of the frequencies in order to preserve the underlying astrophysical content behind such positions. They are reported for epoch 2015.0 and must be propagated for observations at other epochs for the most accurate needs, accounting for the acceleration toward the Galactic center, which results in a dipolar proper motion field of amplitude 0.0058 milliarcsecond yr−1 (mas yr−1). The frame is aligned onto the International Celestial Reference System to within the accuracy of ICRF2 and shows a median positional uncertainty of about 0.1 mas in right ascension and 0.2 mas in declination, with a noise floor of 0.03 mas in the individual source coordinates. A subset of 500 sources is found to have extremely accurate positions, in the range of 0.03–0.06 mas, at the traditional 8.4 GHz frequency. Comparing ICRF3 with the recently released Gaia Celestial Reference Frame 2 in the optical domain, there is no evidence for deformations larger than 0.03 mas between the two frames, in agreement with the ICRF3 noise level. Significant positional offsets between the three ICRF3 frequencies are detected for about 5% of the sources. Moreover, a notable fraction (22%) of the sources shows optical and radio positions that are significantly offset. There are indications that these positional offsets may be the manifestation of extended source structures. This third realization of the ICRF was adopted by the IAU at its 30th General Assembly in August 2018 and replaced the previous realization, ICRF2, on January 1, 2019.

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Gaia science alerts and the observing facilities of the Serbian-Bulgarian mini-network telescopes

Serbian Astronomical Journal ◽

10.2298/saj1488085d ◽

2014 ◽

pp. 85-93 ◽

Cited By ~ 1

Author(s):

G. Damljanovic ◽

O. Vince ◽

S. Boeva

Keyword(s):

Active Galactic Nuclei ◽

Reference Frame ◽

European Space Agency ◽

Galactic Nuclei ◽

Long Baseline ◽

Space Agency ◽

Optical Domain ◽

Celestial Reference Frame ◽

Astronomical Station

The astrometric European Space Agency (ESA) Gaia mission was launched in December 19, 2013. One of the tasks of the Gaia mission is production of an astrometric catalog of over one billion stars and more than 500000 extragalactic sources. The quasars (QSOs), as extragalactic sources and radio emitters, are active galactic nuclei objects (AGNs) whose coordinates are well determined via Very Long Baseline Interferometry (VLBI) technique and may reach sub-milliarcsecond accuracy. The QSOs are the defining sources of the quasi-inertial International Celestial Reference Frame (ICRF) because of their core radio morphology, negligible proper motions (until sub-milliarcsecond per year), and apparent point-like nature. Compact AGNs, visible in optical domain, are useful for a direct link of the future Gaia optical reference frame with the most accurate radio one. Apart from the above mentioned activities, Gaia has other goals such as follow-up of transient objects. One of the most important Gaia's requirements for photometric alerts is a fast observation and reduction response, that is, submition of observations within 24 hours. For this reason we have developed a pipeline. In line with possibilities of our new telescope (D(cm)/F(cm)=60/600) at the Astronomical Station Vidojevica (ASV, of the Astronomical Observatory in Belgrade), we joined the Gaia-Follow-Up Network for Transients Objects (Gaia-FUN-TO) for the photometric alerts. Moreover, in view of the cooperation with Bulgarian colleagues (in the frst place, SV), one of us (GD) initiated a local mini-network of Serbian { Bulgarian telescopes useful for the Gaia-FUN-TO and other astronomical purposes. During the next year we expect a new 1.4 m telescope at ASV site. The speed of data processing (from observation to calibration server) could be one day. Here, we present an overview of our activities in the Gaia-FUN-TO which includes establishing Serbian { Bulgarian mini-network (of five telescopes at three sites, ASV in Serbia, Belogradchik and Rozhen in Bulgaria), the Gaia-FUN-TO test observations, and some results.

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The radio structure of the narrow-line Seyfert 1 Mrk 783 with VLBA and e-MERLIN

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3024 ◽

2020 ◽

Vol 499 (3) ◽

pp. 3149-3157

Author(s):

E Congiu ◽

P Kharb ◽

A Tarchi ◽

M Berton ◽

A Caccianiga ◽

...

Keyword(s):

Position Angle ◽

Optical Observations ◽

Narrow Line ◽

Radio Structure ◽

Long Baseline ◽

New Radio ◽

The Galaxy ◽

L Band ◽

Very Long Baseline Array ◽

Band Image

ABSTRACT In this paper, we present the analysis of new radio and optical observations of the narrow-line Seyfert 1 galaxy Mrk 783. $1.6\, \mathrm{GHz}$ observations performed with the e-MERLIN interferometer confirm the presence of the diffuse emission previously observed. The Very Long Baseline Array (VLBA) also detects the nuclear source both at $1.6\, \mathrm{GHz}$ (L band) and $5\, \mathrm{GHz}$ (C band). While the L-band image shows only an unresolved core, the C-band image shows the presence of a partially resolved structure at a position angle of 60○. The brightness temperature of the emission in both bands (${\gt}10^6\, \mathrm{K}$) suggests that it is a pc-scale jet produced by the active galactic nucleus. The relatively steep VLBA spectral index (αVLBA = 0.63 ± 0.03) is consistent with the presence of optically thin emission on milliarcsecond scales. Finally, we investigated two possible scenarios that can result in the misalignment between the kpc and pc-scale radio structure detected in the galaxy. We also analysed the optical morphology of the galaxy, which suggests that Mrk 783 underwent a merging in relatively recent times.

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The First VERA Astrometry Catalog

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/psaa018 ◽

2020 ◽

Vol 72 (4) ◽

Cited By ~ 6

Author(s):

Tomoya Hirota ◽

◽

Takumi Nagayama ◽

Mareki Honma ◽

Yuuki Adachi ◽

...

Keyword(s):

Spiral Structure ◽

Galactic Center ◽

Rapid Variation ◽

Error Sources ◽

Long Baseline ◽

Circular Rotation ◽

Motion Measurements ◽

Very Long Baseline Array ◽

Source Structure ◽

Maser Sources

Abstract We present the first astrometry catalog from the Japanese VLBI (very long baseline interferometer) project VERA (VLBI Exploration of Radio Astrometry). We have compiled all the astrometry results from VERA, providing accurate trigonometric-annual-parallax and proper-motion measurements. In total, 99 maser sources are listed in the VERA catalog. Among them, 21 maser sources are newly reported, while the rest of the 78 sources are referred to in previously published results or those in preparation for forthcoming papers. The accuracy in the VERA astrometry is revisited and compared with that from the other VLBI astrometry projects such as BeSSeL (The Bar and Spiral Structure Legacy) Survey and GOBELINS (the Gould’s Belt Distances Survey) with the VLBA (Very Long Baseline Array). We have confirmed that most of the astrometry results are consistent with each other, and the largest error sources are due to source structure of the maser features and their rapid variation, along with the systematic calibration errors and different analysis methods. Combined with the BeSSeL results, we estimate the up-to-date fundamental Galactic parameters of $R_{0}=7.92\pm 0.16_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$kpc and $\Omega _{\odot }=30.17\pm 0.27_{\rm {stat.}}\pm 0.3_{\rm {sys.}}\:$km$\:$s$^{-1}\:$kpc$^{-1}$, where $R_{0}$ and $\Omega _{\odot }$ are the distance from the Sun to the Galactic center and the Sun’s angular velocity of the Galactic circular rotation, respectively.

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The use of astronomy VLBA campaign MOJAVE for geodesy

Journal of Geodesy ◽

10.1007/s00190-021-01551-3 ◽

2021 ◽

Vol 95 (9) ◽

Author(s):

Hana Krásná ◽

Leonid Petrov

Keyword(s):

Baseline Length ◽

Earth Orientation Parameters ◽

Earth Orientation ◽

Long Baseline ◽

Station Coordinates ◽

The Difference ◽

Very Long Baseline Array ◽

Orientation Parameters ◽

Source Structure ◽

Selection Of

AbstractWe investigated the suitability of the astronomical 15 GHz Very Long Baseline Array (VLBA) observing program MOJAVE-5 for estimation of geodetic parameters, such as station coordinates and Earth orientation parameters. We processed a concurrent dedicated VLBA geodesy program observed at 2.3 GHz and 8.6 GHz starting on September 2016 through July 2020 as reference dataset. We showed that the baseline length repeatability from MOJAVE-5 experiments is only a factor of 1.5 greater than from the dedicated geodetic dataset and still below 1 ppb. The wrms of the difference of estimated Earth orientation parameters with respect to the reference IERS C04 time series are a factor of 1.3 to 1.8 worse. We isolated three major differences between the datasets in terms of their possible impact on the geodetic results, i.e. the scheduling approach, treatment of the ionospheric delay, and selection of target radio sources. We showed that the major factor causing discrepancies in the estimated geodetic parameters is the different scheduling approach of the datasets. We conclude that systematic errors in MOJAVE-5 dataset are low enough for these data to be used as an excellent testbed for further investigations on the radio source structure effects in geodesy and astrometry.

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