The Third VLBA Calibrator Survey: VCS3

Petrov, Leonid; Kovalev, Y. Y.; Fomalont, Ed; Gordon, D.

doi:10.1086/426920

Cited by 154 publications

(175 citation statements)

References 23 publications

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“…4) -systematically lower than the one measured in the parsec-scale cores of typical bright extragalactic Doppler-boosted core-jet sources (e.g., Kovalev et al 2005;Pushkarev & Kovalev 2011, in prep.). The .…”

Section: Properties Of the Dominating Parsec-scale Componentsmentioning

confidence: 73%

“…(11) Comments: COINS -the source is part of the COINS (Peck & Taylor 2000); COINS-REJ -the source was considered as a candidate for the COINS sample but was rejected (Peck & Taylor 2000); GPS -GPS source, part of the RATAN-600 GPS sample Sokolovsky et al (2009) unless indicated otherwise, for these sources approximate spectral peak frequency (in GHz) is indicated; GPS-REJ the source was reported in the literature as a GPS candidate, but was not confirmed by RATAN-600 observations; STEEP -steep spectrum source, FLAT -flat spectrum source. (12) To distinguish between resolved and unresolved components we use the criterium proposed by Kovalev et al 2005: ψ > HPBW 4 ln 2 π ln SNR SNR−1 where ψ is the component best-fit angular size, HPBW is the Half Power Beam Width, SNR is the signal to noise ratio of the component. (13) No RATAN-600 observations available for this source.…”

Section: Discussionmentioning

confidence: 99%

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VLBI-selected sample of compact symmetric object candidates and frequency-dependent position of hotspots

Sokolovsky¹,

Kovalev²,

Pushkarev³

et al. 2011

A&A

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Context. The compact symmetric objects (CSOs) are small (<1 kiloparsec) and powerful extragalactic radio sources showing emission on both sides of an active galactic nucleus and no signs of strong relativistic beaming. They may be young radio sources, progenitors of large FR II radio galaxies. Aims. We aim to study the statistical properties of CSOs by constructing and investigating a new large sample of CSO candidates on the basis of dual-frequency, parsec-scale morphology. Methods. For the candidate selection we utilized VLBI data for 4170 extragalactic objects obtained simultaneously at 2.3 and 8.6 GHz (S and X band) within the VLBA Calibrator Survey 1-6 and the Research and Development -VLBA projects. Properties of their broad-band radio spectra were characterized by using RATAN-600 observations. Numerical modeling was applied in an attempt to explain the observed effects. Results. A sample of 64 candidate CSOs is identified. The median two-point S -X band spectral index of parsec-scale hotspots is found to be −0.52; with the median brightness temperature ∼10 9 K at X band. Statistical analysis reveals a systematic difference between positions of brightest CSO components (associated with hotspots) measured in the S and X bands. The distance between these components is found to be on average 0.32 ± 0.06 mas greater at 8.6 GHz than at 2.3 GHz. Conclusions. This difference in distances cannot be explained by different resolutions at the S and X bands. It is a manifestation of spectral index gradients across CSO components, which may potentially provide important physical information about them. Despite our detailed numerical modeling of a CSO hotspot, the model was not able to reproduce the magnitude of the observed positional difference. A more detailed modeling may shed light on the origin of the effect. Multifrequency follow-up VLBI observations of the selected sample are needed to confirm and study newly identified CSOs from the list presented here.

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Section: Properties Of the Dominating Parsec-scale Componentsmentioning

confidence: 73%

Section: Discussionmentioning

confidence: 99%

VLBI-selected sample of compact symmetric object candidates and frequency-dependent position of hotspots

Sokolovsky¹,

Kovalev²,

Pushkarev³

et al. 2011

A&A

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“…These sources are mainly drawn from the Radio Fundamental Catalogue (RFC) comprising all sources observed with VLBI for astrometry and geodesy programmes. They also include data from major VLBI surveys such as the VLBA Calibrator Survey (e.g., Beasley et al 2002;Petrov et al 2005;Kovalev et al 2007), the VLBI Imaging and Polarimetry Survey (Helmboldt et al 2007;Petrov & Taylor 2011), and the VLBA 2-cm Survey Kellermann et al (1998Kellermann et al ( , 2004, among others. For their sample of sources, they fit two circular Gaussian components to the self-calibrated visibilities for each source, then select the most compact component as the core component for which they determine the FWHM angular sizes.…”

Section: Published Vlbi Core Sizesmentioning

confidence: 99%

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

Koay

Macquart

Jauncey

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We investigate the relationship between 5 GHz interstellar scintillation (ISS) and 15 GHz intrinsic variability of compact, radio-selected AGNs drawn from the Microarcsecond Scintillation-Induced Variability (MASIV) Survey and the Owens Valley Radio Observatory (OVRO) blazar monitoring program. We discover that the strongest scintillators at 5 GHz (modulation index, m 5 ≥ 0.02) all exhibit strong 15 GHz intrinsic variability (m 15 ≥ 0.1). This relationship can be attributed mainly to the mutual dependence of intrinsic variability and ISS amplitudes on radio core compactness at ∼ 100 µas scales, and to a lesser extent, on their mutual dependences on source flux density, arcsec-scale core dominance and redshift. However, not all sources displaying strong intrinsic variations show high amplitude scintillation, since ISS is also strongly dependent on Galactic line-of-sight scattering properties. This observed relationship between intrinsic variability and ISS highlights the importance of optimizing the observing frequency, cadence, timespan and sky coverage of future radio variability surveys, such that these two effects can be better distinguished to study the underlying physics. For the full MASIV sample, we find that Fermi-detected gamma-ray loud sources exhibit significantly higher 5 GHz ISS amplitudes than gamma-ray quiet sources. This relationship is weaker than the known correlation between gamma-ray loudness and the 15 GHz variability amplitudes, most likely due to jet opacity effects.

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“…The ICRF2 consists of a catalog with the VLBI coordinates of 3414 extragalactic radio sources (from which 295 are defining sources). It was constructed from all geodetic and astrometric VLBI data acquired so far, including those from the Very Long Baseline Array (VLBA) Calibrator Survey (VCS; Beasley et al 2002;Fomalont et al 2003;Petrov et al 2005Petrov et al , 2006Kovalev et al 2007;Petrov et al 2008). It has a noise floor in position of about 60 μas and an axis stability of 10 μas.…”

Section: Introductionmentioning

confidence: 99%

VLBI observations of optically-bright extragalactic radio sources for the alignment of the radio frame with the future Gaia frame

Bourda

Charlot

Porcas

et al. 2010

A&A

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Context. The European space astrometry mission Gaia will construct a dense optical QSO-based celestial reference frame. For consistency between optical and radio positions, it will be important to align the Gaia and VLBI frames with the highest possible accuracy. It has been found that only 70 (10%) of the sources from the International Celestial Reference Frame (ICRF) are suitable for establishing this link, either because they are not bright enough at optical wavelengths or because they have significant extended radio emission which precludes reaching the highest astrometric accuracy. Aims. In order to improve the situation, we have initiated a VLBI survey dedicated to finding additional suitable radio sources for aligning the two frames. Methods. The sample consists of 447 optically-bright (magnitude ≤18) extragalactic radio sources, typically 20 times weaker than the ICRF sources, which have been selected by cross-correlating an optical quasar catalog with the NRAO VLA Sky Survey (NVSS).Results. This paper presents the observing strategy to detect, image, and measure accurate radio positions for these sources. It also provides results on the VLBI detectability of the sources, as derived from initial observations with the European VLBI Network in June and October 2007. Based on these observations, a high detection rate of 89% is found, which is promising for the continuation of this project. This high VLBI detection rate for sources from the NVSS catalog is probably due to the selection process, suggesting that optically-bright quasars have compact radio structures.

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The Third VLBA Calibrator Survey: VCS3

Cited by 154 publications

References 23 publications

VLBI-selected sample of compact symmetric object candidates and frequency-dependent position of hotspots

VLBI-selected sample of compact symmetric object candidates and frequency-dependent position of hotspots

The MASIV Survey – IV. Relationship between intra-day scintillation and intrinsic variability of radio AGNs

VLBI observations of optically-bright extragalactic radio sources for the alignment of the radio frame with the future Gaia frame

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