Optical–Radio Position Offsets Are Inversely Correlated with AGN Photometric Variability

Secrest, Nathan J.

doi:10.3847/2041-8213/ac8d5d

Cited by 8 publications

(17 citation statements)

References 30 publications

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“…collectively called GCRF; Gaia Collaboration et al 2018Collaboration et al , 2022 in the optical. As mentioned previously, there are also notable VLBI-Gaia positional offsets (Mignard et al 2016;Kovalev et al 2017;Charlot et al 2020;Liu et al 2021;Secrest 2022). Observations of radio stars are helpful to tie together these international celestial reference frames (Reid & Honma 2014; Malkin 2016, for more details see Section 3.3.3).…”

Section: Radio Stars: Vlbi Versus Gaia Parallaxesmentioning

confidence: 88%

VLBI with SKA: Possible Arrays and Astrometric Science

Li,

Xu,

et al. 2024

Res. Astron. Astrophys.

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The next generation of very long baseline interferometry (VLBI) is stepping into the era of microarcsecond ($\mu$as) astronomy, and pushing astronomy, especially astrometry, to new heights. VLBI with the Square Kilometre Array (SKA), SKA-VLBI, will increase current sensitivity by an order of magnitude, and reach astrometric precision routinely below 10 $\mu$as, even challenging 1 $\mu$as. This advancement allows precise parallax and proper motion measurements of various celestial objects. Such improvements can be used to study objects (including isolated objects, and binary or multiple systems) in different stellar stages (such as star formation, main-sequence stars, asymptotic giant branch stars, pulsars, black holes, white dwarfs, etc.), unveil the structure and evolution of complex systems (such as the Milky Way), benchmark the international celestial reference frame, and reveal cosmic expansion. Furthermore, the theory of general relativity can also be tested with SKA-VLBI using precise measurements of light deflection under the gravitational fields of different solar system objects and the perihelion precession of solar system objects.

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Section: Radio Stars: Vlbi Versus Gaia Parallaxesmentioning

confidence: 88%

VLBI with SKA: Possible Arrays and Astrometric Science

Li,

Xu,

et al. 2024

Res. Astron. Astrophys.

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“…However, these prescriptions turn out to be either overly restrictive or require additional astrophysical information that is currently unavailable. For example, highly variable blazar sources have recently been shown to exhibit optical-radio position offsets far less frequently than their less variable radio-loud counterparts (Secrest 2022), probably due to the smaller line-of-sight angles of their radio jets. Unfortunately, the fraction of blazars in ICRF3 (and generally on the sky) is too small to be exclusively used as a basis of a multifrequency CRF.…”

Section: Discussionmentioning

confidence: 99%

“…Our approach is also based on the assumption that the astrophysical radio-optical offsets are not skycorrelated. Secrest (2022) predicted that non-blazar sources that are not currently exhibiting significant optical-radio offsets, which constitute the majority of ICRF3, are more likely to develop offsets in the future, which further underscores the need for continuous monitoring.…”

Section: Discussionmentioning

confidence: 99%

Radio-optical Reference Catalog, Version 1

Макаров¹,

Johnson²,

Secrest³

2023

Self Cite

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The fundamental celestial reference frame (CRF) is based on two catalogs of astrometric positions: the third realization of the International Celestial Reference Frame (ICRF3), and the much larger Gaia CRF, built from the third data release (DR3). The objects in common between these two catalogs are mostly distant AGNs and quasars that are both sufficiently optically bright for Gaia and radio loud for the VLBI. This limited collection of reference objects is crucially important for the mutual alignment of the two CRFs and the maintenance of all of the other frames and coordinate systems branching from the ICRF. In this paper, we show that the three components of ICRF3 (S/X, K, and X/Ka band catalogs) have significantly different sky-correlated vector fields of position offsets with respect to Gaia DR3. When iteratively expanded in the vector spherical harmonics up to degree 4 on a carefully vetted set of common sources, each of these components includes several statistically significant terms. The median sky-correlated offsets from the Gaia positions are found to be 56 μas for the S/X, 100 μas for the K, and 324 μas for the X/Ka catalogs. The weighted mean vector field is subtracted from the Gaia reference positions, while the deviations from that field are added to each of the ICRF3 components. The corrected positions from each of the four input catalogs are combined into a single weighted mean catalog, which we propose to be the current most accurate realization of an inertial radio-optical CRF.

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“…Fortunately, due to differences in the way the BP and RP photometry is handled compared to the G photometry, extended objects will have a flux excess in G BP + G RP when compared to G beyond that expected from differences in passband. This is captured in the Gaia catalog as the BP/RP flux excess factor, and we require that it be less than 2 to ensure that only compact objects are assigned Gaia photometry (e.g., Secrest 2022). The G, G BP , and G RP magnitudes are on the Vega system.…”

Section: Opticalmentioning

confidence: 99%

LQAC-6: Sixth Release of the Large Quasar Astrometric Catalogue

Souchay,

Secrest,

Sexton

et al. 2024

A&A

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Context. In addition to being objects of intense interest for cosmology and studies of the evolution of the universe, quasars are used to define quasi-inertial positions on the celestial sphere. Since its first publication in 2009, the purpose of the Large Quasar Astrometric Catalogue (LQAC) has been to provide the largest catalogue of bona fide quasars suitable for astrometry, with the high-precision positions from Gaia becoming available in the fourth release (LQAC-4). Aims Following the same kind of procedure as in the previous releases of the LQAC, our aim is to compile the maximum number of recorded quasars, with optimised equatorial coordinates and fundamental information about their physical properties such as the redshift, the photometry, radio fluxes, morphological index. Methods New quasars from the SDSS DR16Q release were cross-matched with the precedent LQAC-5 compilation with a 1" radius, which leads to 225 082 objects not present in the previous LQAC-5 release. Another cross-match was done with the Gaia Celestial Reference Frame 3 (GCRF3) catalogue, which is itself a compilation of a large number of quasars catalogues, accompanied with very accurate Gaia DR3 positions. Moreover, AGN's coming from 19 individual extragalactic surveys not considered in the previous LQAC compilations are added Results This new LQAC-6 release contains 2 073 099 objects, which is 3.5 times the number of objects recorded in the previous LQAC-5 release. Among them, 1 739 187 objects were found in common with the Gaia DR3, within a 1" search radius. A large part of new objects belong to the GCRF3 catalogue, which gathers a total number of 1 614 218 objects Conclusion The LQAC-6 delivers a nearly complete catalogue of quasars and AGN's to the astronomical community, with the aim of giving their best equatorial coordinates with respect to the recent ICRF3 and with exhaustive additional information. For as much as $83.9 <!PCT!>$ of the sample, these coordinates are extracted from the very recent Gaia DR3.

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Optical–Radio Position Offsets Are Inversely Correlated with AGN Photometric Variability

Cited by 8 publications

References 30 publications

VLBI with SKA: Possible Arrays and Astrometric Science

VLBI with SKA: Possible Arrays and Astrometric Science

Radio-optical Reference Catalog, Version 1

LQAC-6: Sixth Release of the Large Quasar Astrometric Catalogue

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