Absolute kinematics of radio source components  
 in the complete S5 polar cap sample

Martí-Vidal, Iván; Marcaide, J. M.; Guirado, J. C.; Ros, E.

doi:10.1051/0004-6361:20078067

Cited by 13 publications

(10 citation statements)

References 13 publications

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“…with dedicated VLBI astrometry observations (cf., Guirado et al 1995;Martí-Vidal et al 2008). Based on the analysis of these factors (Guirado et al 1995), we can expect that their contribution to the positional errors should be within…”

Section: Astrometry and Proper Motion Of The Pulsarmentioning

confidence: 99%

VLBI imaging of a flare in the Crab nebula: more than just a spot

Lobanov

Horns

Muxlow

2011

A&A

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We report on very long baseline interferometry (VLBI) observations of the radio emission from the inner region of the Crab nebula, made at 1.6 GHz and 5 GHz after a recent high-energy flare in this object. The 5 GHz data have provided only upper limits of 0.4 milli-Jansky (mJy) on the flux density of the pulsar and 0.4 mJy/beam on the brightness of the putative flaring region. The 1.6 GHz data have enabled imaging the inner regions of the nebula on scales of up to ≈40 . The emission from the inner "wisps" is detected for the first time with VLBI observations. A likely radio counterpart (designated "C1") of the putative flaring region observed with Chandra and HST is detected in the radio image, with an estimated flux density of 0.5 ± 0.3 mJy and a size of 0 . 2-0 . 6. Another compact feature ("C2") is also detected in the VLBI image closer to the pulsar, with an estimated flux density of 0.4 ± 0.2 mJy and a size smaller than 0 . 2. Combined with the broad-band SED of the flare, the radio properties of C1 yield a lower limit of ≈0.5 mG for the magnetic field and a total minimum energy of 1.2 × 10 41 erg vested in the flare (corresponding to using about 0.2% of the pulsar spin-down power). The 1.6 GHz observations provide upper limits for the brightness (0.2 mJy/beam) and total flux density (0.4 mJy) of the optical Knot 1 located at 0 . 6 from the pulsar. The absolute position of the Crab pulsar is determined, and an estimate of the pulsar proper motion (μ α = −13.0 ± 0.2 mas/yr, μ δ = +2.9 ± 0.1 mas/yr) is obtained.

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Section: Astrometry and Proper Motion Of The Pulsarmentioning

confidence: 99%

VLBI imaging of a flare in the Crab nebula: more than just a spot

Lobanov

Horns

Muxlow

2011

A&A

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“…This may indeed be possible but one should note that the relative positions measured at 8.4 GHz between ICRF sources will not correspond to their relative positions measured using group-delays at 8.4 GHz. Marti-Vidal et al (2008) have used wide-field phasedifferenced observations at 15.4 GHz, and an atmospheric model, to determine positions for 13 AGN cores in the S5 polar cap sample, with quoted precisions ranging from 14−200 μas. They determined mean position corrections with respect to ICRF group-delay positions of 278 μas in RA and 170 μas in declination.…”

Section: Phase-reference Observationsmentioning

confidence: 99%

Radio astrometry with chromatic AGN core positions

Porcas¹

2009

A&A

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Aims. The effect of frequency-dependent AGN core positions ("core-shifts") on radio Very Long Baseline Interferometry (VLBI) global astrometry measurements is investigated. Methods. The basic equations relating to VLBI astrometry are reviewed, including the effects of source structure. A power-law representation of core-shifts, based on both observations and theoretical considerations of jet conditions, is incorporated. Results. It is shown that, in the presence of core-shifts, phase and group-delay astrometry measurements yield different positions. For a core displacement from the jet base parametrized by Δx(λ) = kλ β , group delays measure a "reduced" core-shift of (1 − β)Δx(λ). For the astrophysically-significant case of β = 1, group delays measure no shift at all, giving the position of the jet base. At 8.4 GHz an estimated typical offset between phase and group-delay positions of ∼170 μas is smaller than the current ∼250 μas precision of group-delay positions of the sources used to define the ICRF; however, this effect must be taken into account for future measurements planned with improved accuracy when comparing with optical positions of AGN to be obtained with the GAIA mission.

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“…The procedure of phase connection in our astrometric analysis is described in Martí-Vidal et al (2008). It is based on previous approaches (e.g.…”

Section: The Phase Connectionmentioning

confidence: 99%

“…See Martí-Vidal et al (2008), and references therein, for details of the uvpap model. The main improvements of uvpap include the use of the JPL ephemeris binary tables and the upgrade of relativistic effects of the Solar System bodies, computed using the Consensus Model (McCarthy & Petit 2003).…”

Section: The University Of Valencia Precision Astrometry Package (Uvpap)mentioning

confidence: 99%

“…It is based on previous approaches (e.g. Shapiro et al 1979, Guirado et al 1995, but with some substantial differences such as the use of an in-house developed automatic connection algorithm, described in Martí-Vidal et al (2008), that corrects unmodelled phase-delay cycles imposing the nullity of all the closure phases. The use of this algorithm, or a similar one, is mandatory for a correct phase connection, given the large amount of data from many sources and antennas involved in our observations.…”

Section: The Phase Connectionmentioning

confidence: 99%

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Multi-wavelength VLBI phase-delay astrometry of a complete sample of radio sources

Martí-Vidal¹,

Marcaide²,

Guirado³

2007

Proc. IAU

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Abstract. We report on the first global high-precision (differential phase-delay) astrometric analyses performed on a complete set of radio sources. We have observed the S5 polar cap sample, consisting of 13 quasars and BL Lac objects, with the VLBA at 8.4, 15, and 43 GHz. We have developed new algorithms to enable the use of the differential phase-delay observable in global astrometric observations. From our global analyses, we determine the relative positions between all pairs of sources with typical precisions ranging from 10 to 200 µas, depending on observing frequency and source separation. In this paper, we discuss the impact of this observable in the enhancement of the astrometric precision. Since a large fraction of the S5 polar cap sources are ICRF defining sources, this may result in a test of the ICRF stability. Our multi-epoch / multi-frequency approach will also provide both absolute kinematics and spectral information of all sources in the sample. In turn, this will provide an important check on key predictions of the standard jet interaction model.

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Absolute kinematics of radio source components in the complete S5 polar cap sample

Cited by 13 publications

References 13 publications

VLBI imaging of a flare in the Crab nebula: more than just a spot

VLBI imaging of a flare in the Crab nebula: more than just a spot

Radio astrometry with chromatic AGN core positions

Multi-wavelength VLBI phase-delay astrometry of a complete sample of radio sources

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