The point source OQ208 was used to determine the antenna-based phase corrections. 3C 286 was used as the primary flux-density calibrator and JVAS B2103+213 was used for phase-referencing. The same set-up was used for both observations. In order to determine if any of the compact components detected by the VLA showed extended emission at higher resolutions we observed CLASS B2108+213 with MERLIN at 5 GHz for ∼1.5 h on 2000 March 10 and ∼9 h on 2001 August 10. CLASS B2108+213, with a maximum image separation of 4.56 arcsec, is the widest separation gravitational lens system in the CLASS sample. The image separation distribution of the 22 CLASS gravitational lenses. However, CLASS B2108+213 was followed up as a promising lens candidate even though it was no longer part of the statistically well-defined CLASS sample. Therefore, CLASS B2108+213 failed to meet the strict lens candidate selection criteria due to its total integrated 8.46-GHz flux density being less than 20 mJy. The total integrated flux density of the system at 8.46 GHz is 18.5 mJy and the flux-density ratio between the brightest and faintest components is ∼8 : 1. 2 for the CLASS gravitational lens image separation distribution). With an image separation between components A and B of 4.56 arcsec, CLASS B2108+213 has a wider image separation than any gravitational lens system thus far discovered by CLASS (see Fig. 1, whose flux densities and relative positions are given in Tables 1 and 2, respectively. The VLA detected three compact components, shown in Fig. The rms noise level was 180 μJy beam −1 and the beam size was 0.26 × 0.23 arcsec 2. The uv-data were naturally weighted and elliptical Gaussian model components were fitted to each image. The data were edited and calibrated in the standard way using aips (Astronomical Image Processing Software) and imaged within the Caltech VLBI difference mapping package ( difmap Shepherd 1997) using the CLASS mapping script ( Myers et al. 3C 286 was chosen as the primary flux-density calibrator and phase-referencing was carried out with JVAS B2059+034 (Jodrell Bank VLA Astrometric Survey Patnaik et al. A 3.3-s correlator integration time with two 50-MHz IFs was used. The total on-source integration time was ∼30 s. 2 Radio Observations 2.1 VLA 8.46-GHz observationĬLASS B2108+213 was observed with the VLA in A configuration at 8.46 GHz as part of the final phase of CLASS on 1999 August 17. For all calculations we adopt an Ω M= 0.3, Ω Λ= 0.7 flat Universe, with a Hubble parameter of H 0= 70 km s −1 Mpc −1. Finally, in Section 5 we summarize our findings and outline the future work we intend to carry out on this intriguing new gravitational lens from CLASS. Using the available observational data, the lensing hypothesis, along with an analysis of the lensing potential, is discussed in Section 4. Follow-up optical and infrared imaging of the system and the surrounding field, taken with the Hubble Space Telescope, is presented in Section 3. In Section 2 we describe the VLA, MERLIN and VLBA radio observations which led to the discovery of the gravitational lens candidate CLASS B2108+213. In this paper, we present observations of the gravitational lens candidate CLASS B2108+213, which was discovered during the fourth and final phase of CLASS. 2003 and references therein for a discussion of all the gravitational lenses discovered by CLASS). The detection of compact structure and extended emission in the multiple components at higher resolutions with MERLIN (Multi-Element Radio Linked Interferometer Network) and the VLBA (Very Long Baseline Array) confirmed the lensing hypothesis for 21 gravitational lenses during the first three phases of CLASS (see Browne et al.
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CLASS sources were identified as promising gravitational lens candidates if the VLA 8.46-GHz image contained multiple compact components with Gaussian full width at half maximum (FWHM) ≤ 170 mas, the image separations were in the range 0.3 ≤Δθ≤ 15 arcsec, the total integrated flux density was S 8.46≥ 20 mJy and the component flux-density ratio was ≤10 : 1. The 0.2-arcsec angular resolution provided by the VLA allowed the straightforward identification of galaxy-scale gravitational lenses, which typically have image separations of ∼1 arcsec. A complete sample of 11 685 flat-spectrum radio sources ( S ν∝ν α where α≥−0.5 between 1.4 and 4.85 GHz) was observed with the Very Large Array (VLA) in A configuration at 8.46 GHz between 19. 2003) is the largest statistically complete gravitational lens survey ever undertaken. The Cosmic Lens All-Sky Survey (CLASS Browne et al. Gravitational lensing, quasars: individual: CLASS B2108+213, cosmology: observations 1 Introduction
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