The time delay of JVAS B1030+074 from VLA polarization monitoring
  We have analysed archival 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 ($<$5d) 90-degree rotation event.
Our best estimate of the time delay is $146\pm6$d (1$\sigma$), 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 $H_0$, for example through a detection of the lensed source's VLBI 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 ISM of the
lensing galaxies or the Galaxy.
