The Time Delay of Gravitational Lens 0957+561. II. Analysis of Radio Data and Combined Optical-Radio Analysis

The method for determining the time delay of gravitational lens 0957+561, which we previously applied to published optical data, is here extended and applied to the radio data of Lehar et al. The radio data are relatively free of the windowing effects of seasonal observing. For the radio data alone, our analysis gives the result τ_AB = 548⁺¹⁹_-16 days (95% C.L.). Combined analysis of the optical and radio data yield τ_AB = 540±12 days (95% C.L.). We have also fitted for a linear drift between the two components (possibly an indication of microlensing). The radio data are consistent with zero drift (as expected theoretically), while the optical data show a small but marginally significant drift at the 2.4 σ level.