A method for efficient measurement of gravitational lens time delays
  The Hubble constant value is currently known to 10% accuracy unless
assumptions are made for the cosmology (Sandage et al. 2006). Gravitational
lens systems provide another probe of the Hubble constant using time delay
measurements. However, current investigations of ~20 time delay lenses, albeit
of varying levels of sophistication, have resulted in different values of the
Hubble constant ranging from 50-80 km/s/Mpc. In order to reduce uncertainties,
more time delay measurements are essential together with better determined mass
models (Oguri 2007, Saha et al. 2006). We propose a more efficient technique
for measuring time delays which does not require regular monitoring with a
high-resolution interferometer array. The method uses double image and
long-axis quadruple lens systems in which the brighter component 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. We present
simulations of this method together with a pilot project using the WSRT
(Westerbork Radio Synthesis Telescope) to trigger VLA (Very Large Array)
observations. This new method is promising for measuring time delays because it
uses relatively small amounts of time on high-resolution telescopes. This will
be important because many SKA pathfinder telescopes, such as MeerKAT (Karoo
Array Telescope) and ASKAP (Australian Square Kilometre Array Pathfinder), have
high sensitivity but limited resolution.
