P.G. Edwards , J.E.J. Lovell , H. Hirabayashi , D.L. Jauncey S. Toft, PASA, 18 (2), in press.
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Introduction
The unexpected discovery in 1979 of the first gravitational lens, 0957+561 (Walsh, Carswell, & Weymann 1979), provided further evidence supporting the General Theory of Relativity and opened the field of gravitational lens studies. Due to the magnification of gravitational lenses, fainter, more distant sources can be observed, and the intervening medium studied. Studies of lensing systems also provide an independent means of estimating the mass of lensing galaxies. In addition, a well characterized lensing system enables H0 to be estimated (see, e.g., Koopmans et al. 2001). Optical and radio surveys of gravitational lenses are approaching the sensitivity required to confirm or reject the best-fit values for cosmological constants obtained from supernovae and other data (Myers 1999), and each well-determined lens system brings this goal closer to fulfilment. The largest uncertainty in most cases is in the model of the lensing system.
B1152+199 was discovered during VLA observations in 1998 as part of the Cosmic Lens All-Sky Survey (Myers et al. 1999). The lens produces two images of a quasar, separated by 1.56'', with a flux density ratio at 8.46GHz of 3.03
0.03. Follow-up optical observations determined the background quasar, at z=1.019, is being lensed by a foreground galaxy at z=0.439 (Myers et al. 1999). A faint, steeper-spectrum, radio source was also detected 23'' from the lensed double, however this appeared to be unrelated (in a lensing sense) to the flat spectrum double. The relatively flat 8 to 15 GHz spectral index, -0.32 (
), makes B1152+199 a strong candidate for time delay studies.
We are undertaking a program of observations of the gravitational lens B1152+199 in order to improve our understanding of the lens system as a step towards the ultimate aim of accurately determining H0 once the time delay for the system has been measured. In Section 2 we present the results from our full-synthesis observation of the lens system, and the evidence for variability in the source components is assessed in Section 3. In Section 4 the results of preliminary modeling of the lens system are given.
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