VLBI Observations of the Gravitational-Lens Images of Q0957+561

We have conducted a series of VLBI observations of the gravitational-lens images of the quasar Q0957+561 (Walsh et al., 1979), utilizing the Mark III VLBI data acquisition system (Rogers et al., 1983). The goals of our observations are to (1) map the milliarcsecond structure of the A and B images, (2) detect the predicted third image of the quasar, and (3) determine the time delay between the images. We will use these results to constrain the mass distribution of the lens and, possibly, cosmological constants.

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The Mark IV VLBI Data-Acquisition and Correlation System

Symposium - International Astronomical Union ◽

10.1017/s0074180900173139 ◽

1993 ◽

Vol 156 ◽

pp. 151-157

Author(s):

Alan R. Whitney

Keyword(s):

Data Acquisition ◽

Cost Effective ◽

Data Acquisition System ◽

Data Rate ◽

Acquisition System ◽

The Past ◽

Vlbi Observations ◽

Data Rates ◽

Correlation System ◽

Vlbi Data

Modern VLBI observations for both astronomy and geodesy continue to demand the utmost in sensitivity. Of the methods potentially available for increasing the sensitivity of continuum VLBI observations, increasing the recorded bandwidth is generally the most cost effective.Over the past two years a broadly-supported program has been underway at Haystack Observatory to increase the sensitivity of the Mark IIIA VLBI system by more than a factor of 2. The result is an upgrade to the existing Mark IIIA data-acquisition system, dubbed Mark IV, which increases the maximum data rate to 1024 Mbits/sec, more than quadrupling the maximum data-rate of the Mark IIIA.A new correlator, based on a new custom VLSI correlator chip is also being designed to support the 1 Gbit/sec data rates from the Mark IV data-acquisition-system. An international collaborative effort is being mounted to help defray the high costs of development.

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Can We Measure H0 with VLBI Observations of Gravitational Images?

Symposium - International Astronomical Union ◽

10.1017/s0074180900134485 ◽

1988 ◽

Vol 129 ◽

pp. 207-208

Author(s):

E. E. Falco ◽

M. V. Gorenstein ◽

I. I. Shapiro

Keyword(s):

Time Delay ◽

Mass Distribution ◽

Velocity Dispersion ◽

Gravitational Lens ◽

Lens System ◽

Relative Time ◽

Surface Mass ◽

A Value ◽

Vlbi Observations ◽

The Difference

We have used the relative positions and magnifications of the A and B images in the gravitational lens system 0957+561, obtained from VLBI observations, to constrain a model for the surface mass distribution of the lens. With measurements of the difference ΔτBA in propagation times associated with A and B (the “relative time delay”) and of the velocity dispersion of the main lensing galaxy, both to be obtained, our model will yield a value for H0 with an uncertainty of ∼ 20% due mainly to uncertainties in our assumptions.

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K-4 VLBI Data-Acquisition System

Publications of the Astronomical Society of Japan ◽

10.1093/pasj/49.6.699 ◽

1997 ◽

Vol 49 (6) ◽

pp. 699-708 ◽

Cited By ~ 10

Author(s):

Hitoshi Kiuchi ◽

Jun Amagai ◽

Shin'ichi Hama ◽

Michito Imae

Keyword(s):

Data Acquisition ◽

Data Acquisition System ◽

Acquisition System ◽

Vlbi Data

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Multi-frequency VLBI Observations of the Gravitational Lens B0218+357

Symposium - International Astronomical Union ◽

10.1017/s0074180900080244 ◽

1996 ◽

Vol 175 ◽

pp. 115-117

Author(s):

R. W. Porcas ◽

A. R. Patnaik

Keyword(s):

Time Delay ◽

Mass Distribution ◽

Hubble Constant ◽

Gravitational Lens ◽

Radio Sources ◽

Constant Independent ◽

Lens System ◽

Vlbi Observations ◽

Spectrum Radio ◽

Simple Mass

The gravitational lens system B0218+357 comprises 2 image components (A and B) and a radio ‘Einstein Ring’ (Patnaik et al, 1993). The redshift of the lens galaxy is 0.6847 (Browne et al, 1994) and that of the imaged source 0.96 (preliminary result; Lawrence et al, 1995). The separation of A and B, which are both flat-spectrum radio sources, is only 0.335 arcsec, leading to the hope that the lens is a single galaxy with a relatively simple mass distribution. Refsdal pointed out (1964) that a model of such a distribution, and a measurement of the time difference along the two image paths, leads to an estimate of the Hubble constant, independent of the usual steps in the distance ladder. B0218+357 is one of only a few lensed systems well suited for such measurements. A preliminary value of 12 days has been measured for the A-B time delay, derived from a comparison of the percentage polarisation variations of the images at 15GHz, using the VLA (Corbett et al, 1995).

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