The time delay of CLASS B1600+434 from VLA multi-frequency and
  polarization monitoring
  We present an analysis of archival multi-frequency Very Large Array
monitoring data of the two-image gravitational lens system CLASS B1600+434,
including the polarization properties at 8.5 GHz. From simulating radio light
curves incorporating realistic external variability in image A, we find time
delays consistent at 1 $\sigma$ for all frequencies and in total flux density
and polarization. The delay with the smallest uncertainty (total flux density
at 8.5 GHz) is $42.3^{+2.0}_{-1.8}$ (random) $\pm 0.5$ (systematic) d
(equivalent to $42.3 \pm 2.1$ d) whereas combining all delay estimates gives a
slightly higher value of $43.6\pm1.2$ d. Both values are lower than the
previously published radio result and inconsistent with that found in the
optical. $H_0$ determination is difficult due to the complicated lensing mass
and the lack of constraints provided by only two images. However, analysis of
archival Very Long Baseline Interferometry data reveals jets in this system for
the first time, the orientations of which provide model constraints. In
addition, extremely sensitive maps made from combining all the monitoring data
reveal faint emission on one side of the lensing galaxy which we speculate
might be the result of a naked-cusp lensing configuration. Finally, we find
clear evidence for external variability in image A on time-scales of days to
years, the frequency-dependence of which supports the previous conclusion that
this is predominantly due to microlensing. External variability seems to be
completely absent in image B and this does not appear to be a consequence of
scatter-broadening in the interstellar medium of the lensing galaxy.
