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A method for efficient measurement of gravitational lensing time delays

Gürkan, Gülay

[Thesis]. Manchester, UK: The University of Manchester; 2011.

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Abstract

This thesis presents an efficient technique for measuring lensing time delays which does not require regular monitoring with a high-resolution interferometer array. This method uses asymmetric double image and long-axis quadruple radio lens systems in which the brighter component(s) varies first and dominates the total flux density. Monitoring the total flux density with low-resolution but high sensitivity radio telescopes provides the variation of the brighter image and is used to trigger high-resolution observations which can then be used to see the variation in the fainter image.The efficiency of this technique was assessed by performing simulations using the Pelt dispersion statistic and artificial light curves. The results of the cross-correlation simulations demonstrated that time delays can be determined to <10% accuracy. Secondly, a pilot project was implemented using Westerbork Radio Synthesis Telescope (WSRT) to trigger Very Large Array (VLA) observations. Total flux monitoring of 8 radio lens systems was conducted using WSRT observations with enough sensitivity to see the variation in the total flux. Among the 8 systems only B1030+074 showed a variability during the total flux monitoring. Then, VLA observations were triggered for B1030+074. We could not catch the variation of the fainter image during the VLA monitoring. However, further cross-correlation simulations were performed to obtain limits for the time delay between the images.