On significance of VLBI/<i>Gaia</i> position offsets

Petrov, Leonid; Kovalev, Y. Y.

doi:10.1093/mnrasl/slx001

Cited by 54 publications

(20 citation statements)

References 32 publications

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“…The RFC catalogue is derived using all VLBI observations under astrometric programs publicly available by August 01 2018. We used the same procedure of matching Gaia objects against the VLBI catalogue described in detail in Petrov & Kovalev (2017a) and got 9081 matches with the probability of false association below the 2 · 10 −4 level. The immediate comparison of formal uncertainties among matches showed that the Gaia uncertainties are smaller (see Figure 1).…”

Section: Comparison Of Vlbi/gaia Positionsmentioning

confidence: 99%

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

Petrov

Kovalev

Plavin

2018

Monthly Notices of the Royal Astronomical Society

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We have analyzed the differences in positions of 9081 matched sources between the Gaia DR2 and VLBI catalogues. The median position uncertainty of matched sources in the VLBI catalogue is a factor of two larger than the median position uncertainty in the Gaia DR2. There are 9% matched sources with statistically significant offsets between both catalogues. We found that reported positional errors should be re-scaled by a factor of 1.3 for VLBI and 1.06 for Gaia, and in addition, Gaia errors should be multiplied by the square root of chi square per degree of freedom in order to best fit the normalized position differences to the Rayleigh distribution. We have established that the major contributor to statistically significant position offsets is the presence of optical jets. Among the sources for which the jet direction was determined, the position offsets are parallel to the jet directions for 62% of the outliers. Among the matched sources with significant proper motion, the fraction of objects with proper motion directions parallel to jets is a factor of 3 greater than on average. Such sources have systematically higher chi square per degree of freedom. We explain these proper motions as a manifestation of the source position jitter caused by flares that we have predicted earlier. Therefore, the assumption that quasars are fixed points and therefore, differential proper motions determined with respect to quasar photocenters can be regarded as absolute proper motions, should be treated with a great caution.

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Section: Comparison Of Vlbi/gaia Positionsmentioning

confidence: 99%

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

Petrov

Kovalev

Plavin

2018

Monthly Notices of the Royal Astronomical Society

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“…The agreement of the Gaia radio positions and the ICRF3 prototype solution, which was used for this procedure, was reported to be at the level of 20 to 30 µas. For the first Gaia-CRF about 6% of the sources were found to have a significant offset (Mignard, F. et al 2016;Petrov and Kovalev 2017). With the second, more accurate Gaia data re-lease the majority of these offsets were linked to the presence of optical structure because most offsets occur along the jet (Gaia Collaboration, Mignard et al 2018;Plavin et al 2019a;Petrov et al 2019).…”

Section: Gaiamentioning

confidence: 99%

Realization of a multifrequency celestial reference frame through a combination of normal equation systems

Karbon

Nothnagel

2019

A&A

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Context. We present a celestial reference frame (CRF) based on the combination of independent, multifrequency radio source position catalogs using nearly 40 years of Very Long Baseline Interferometry observations at the standard geodetic frequencies at SX band and about 15 years of observations at higher frequencies (K and XKa). The final catalog contains 4617 sources. Aims. We produce a multifrequency catalog of radio source positions with full variance-covariance information across all radio source positions of all input catalogs. Methods. We combined three catalogs, one observed at 8 GHz (X band), one at 24 GHz (K band) and one at 32 GHz (Ka band). Rather than only using the radio source positions, we developed a new, rigorous combination approach by carrying over the full covariance information through the process of adding normal equation systems. Special validation routines were used to characterize the random and systematic errors between the input reference frames and the combined catalog.Results. The resulting CRF contains precise positions of 4617 compact radio astronomical objects, 4536 measured at 8 Ghz, 824 sources also observed at 24 GHz, and 674 at 32 GHz. The frame is aligned with ICRF3 within ±3 µas and shows an average positional uncertainty of 0.1 mas in right ascension and declination. No significant deformations can be identified. Comparisons with Gaia-CRF remain inconclusive, nonetheless significant differences between all frames can be attested.

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“…They propose that 89 of them may be AGNs (quasars and BL Lac) dislodged from their host galaxies' centers. In a much larger study Petrov and Kovalev (2017) used the whole 1.1 billion object dataset from Gaia DR1 and the VLBI absolute astrometry catalog RFC 2016c to find 6,055 secure matches with AGNs. Kovalev et al (2017) used this large sample to check on offsets between radio and optical positions.…”

Section: Quasars In Gaia's First Data Releasementioning

confidence: 99%

Gaia Space Mission and Quasars

Zwitter

2017

Front. Astron. Space Sci.

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On significance of VLBI/Gaia position offsets

Cited by 54 publications

References 32 publications

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

A quantitative analysis of systematic differences in the positions and proper motions of Gaia DR2 with respect to VLBI

Realization of a multifrequency celestial reference frame through a combination of normal equation systems

Gaia Space Mission and Quasars

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