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The Hubble Constant from (CLASS) Gravitational Lenses
L.V.E. Koopmans + the CLASS collaboration, PASA, 18 (2), in press.

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Subsections

Time Delays from CLASS Gravitational Lenses

B0218+357

The GL system B0218+357 was discovered (e.g. Patnaik et al. 1993) as part of the Jodrell Bank-VLA Astrometric Survey (JVAS), which is the brighter subsample (i.e.

$S_{\rm 5\,GHz}$ $\ge$ 200mJy) of the CLASS survey. The system consists of two lensed images of a flat-spectrum radio core, separated by 0.335 arcsec, and an Einstein ring that results from more extended steep-spectrum source structure. The redshift of the source is 0.96, whereas the deflector (a relatively isolated spiral galaxy) has a redshift of 0.68. Corbett et al. (1996) reported a time delay of 12 $\pm$ 3d (1- $\sigma$ error). More recently, Biggs et al. (1999) presented the results from a VLA A-array monitoring campaign. From the percentage linear polarization, polarization angle and 8.5 and 15-GHz flux-density light curves, a time delay of

$\Delta t_{\rm B-A}$ =10.5 $\pm$ 0.4d (95% confidence) was measured. This value was confirmed by Cohen et al. (2001), who find

$\Delta t_{\rm B-A}$ =10.1

^+1.5_-1.6d (95% confidence), using independent data obtained with the VLA during the same period as Biggs et al. (1999).

B1600+434

The GL system B1600+434 (Jackson et al. 1995) consists of two compact flat-spectrum radio images, separated by 1.39 arcsec, of a quasar at a redshift of 1.59. The primary lens galaxy is an edge-on spiral galaxy at a redshift of 0.41 (Jaunsen & Hjorth 1997; Koopmans, de Bruyn & Jackson 1998). An A and B-array VLA 8.5-GHz monitoring campaign gave a time delay of

$\Delta t_{\rm B-A}$ =47⁺¹²_-9d (95% confidence) (Koopmans et al. 2000). More recently, a value of

$\Delta t_{\rm B-A}$ =51 $\pm$ 4d (95% confidence) was found from an optical monitoring campaign with the Nordic Optical Telescope (NOT) (Burud et al. 2000). Preliminary results from a new multi-frequency monitoring campaign with the VLA seem to confirm these results.

B1608+656

The GL system B1608+656 consists of four compact flat-spectrum radio images with a maximum image separation of 2.1 arcsec (Myers et al. 1995). The source has a redshift of 1.39 and is being lensed by two galaxies inside the Einstein radius, of which at least the brightest has a redshift of 0.63. In the optical and near-infrared the host galaxy of the radio source is lensed into prominent arcs (Jackson et al. 1998). Fassnacht et al. (1999) have measured all three time delays from radio light curves obtained in 1996-1997 at 8.5 GHz with the VLA in A and B-array. Combined with data from a similar campaign in 1998, their preliminary results are:

$\Delta t_{\rm B-A}$ =26d,

$\Delta t_{\rm B-C}$ =34d and

$\Delta t_{\rm B-D}$ =73d, with an error of 5d (95% confidence) on each time delay (Fassnacht et al. 2001).

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Title/Abstract Page: The Hubble Constant from
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Contents Page: Volume 18, Number 2

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