A Robust Determination of the Time Delay in 0957+561A,B and a Measurement of the Global Value of Hubble's Constant

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ABSTRACT Continued photometric monitoring of the gravitational lens system 0957+561A,B in the g and r bands with the Apache Point Observatory (APO) 3.5 m telescope during 1996 shows a sharp g band event in the trailing (B) image light curve at the precise time predicted in an earlier paper. The prediction was 1 Supported by the Fannie and John Hertz Foundation 2 Currently at the Kitt Peak National Observatory 3 Currently at the Space Telescope Science Institute -- 2 -- based on the observation of the event during 1995 in the leading (A) image and on a differential time delay of 415 days. This success confirms the so called "short delay", and the absence of any such feature at a delay near 540 days rejects the "long delay" for this system, thus resolving a long standing controversy. A series of statistical analyses of our light curve data yield a best fit delay of 417 Sigma 3 days (95% confidence interval) and demonstrate that this result is quite robust against variations in the analysi...