The radio wave length time delay of gravitational lens 0957+561

摘要

The gravitational lens 0957 + 56l was monitored with the Very Large Array from l979 to 1997. The 6 cm light-curve data from 1995 to l997 and the 4 cm data from l990 to 1997 are reported here. At 4 cm the intrinsic source variations occur earlier and are twice as large as the corresponding variations at 6 cm. The VLBI core and jet components have different magnification factors, leading to different flux ratios for the varying and nonvarying portions of the VLA light curves. Using both the Press, Rybicki, & Hewitt Q (PRHQ) and dispersion statistical techniques, we determined the time delay, core flux ratio, and excess nonvarying B image flux density. The fits were performed for the 4 and 6 cm light curves,both individually and jointly, and we used Gaussian Monte Carlo data to estimate 68 statistical con- fidence levels. The delay estimates from each individual wavelength were inconsistent given the formal uncertainties, suggesting that there are unmodeled systematic errors in the analysis. We roughly estimate the systematic uncertainty in the joint result from the difference between the 6 and 4 cm results, giving 409 ± 30 days for the PRHQ statistic and 397 ± 20 days for the dispersion statistic. These results are consistent with the current optical time delay of 4l7 ± 3 days, reconciling the long-standing difference between the optical and radio 1ight curves and between different statistical analyses. The unmodeled sys- tematic effects may also corrupt light curves for other lenses, and we caution that multiple events at multiple wavelengths may be necessary to determ