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Session 59 - Relativistic Astrophysics.
Oral session, Thursday, January 08
The Cosmic Lens All-Sky Survey (CLASS) is a large-scale search for gravitational lenses among flat-spectrum radio sources. The major goals of the survey are to find lens systems suitable for measuring H_0 and to use lensing statistics to constrain cosmological parameters. Nearly 8000 sources have been observed with the VLA. Six new gravitational lenses have been discovered; in addition, 16 promising lens candidates are currently being investigated. The B1608+656 system was discovered in the first phase of CLASS. The radio map shows four unresolved components arranged in a typical lens morphology. Follow-up observations at optical and infrared wavelengths show the same morphology, as well as the galaxy responsible for the lensing. Both the lens and source redshifts have been determined. WFPC2 images show extended optical emission from the background source that has been lensed into a nearly complete ring. These data are being used to constrain the model of the lensing potential. The system was monitored with the VLA from October 1996 to May 1997, and an event was seen in the light curves of all four components, which allows time delays to be measured. The time delays and improved model give the first measurement of H_0 from a CLASS lens.
Program listing for Thursday