2018MNRAS.481.1000B

We have analysed archival Very Large Array (VLA) 8.4-GHz monitoring data of the gravitational lens system JVAS B1030+074 with the goal of determining the time delay between the two lensed images via the polarization variability. In contrast to the previously published total intensity variations, we detect correlated variability in polarized flux density, percentage polarization, and polarization position angle. The latter includes a fast (<5 d) 90° rotation event. Our best estimate of the time delay is 146 ± 6 d (1σ), considerably longer than that predicted by the lens model presented in the discovery paper. Additional model constraints will be needed before this system can be used to measure H₀, for example through a detection of the lensed source's very long baseline interferometry jet in image B. No time delay is visible in total flux density and this is partially due to much greater scatter in the image B measurements. This must be due to a propagation effect as the radio waves pass through the interstellar medium of the lensing galaxies or the Galaxy.