Extended lens reconstructions with Grale: exploiting time domain,
  substructural and weak-lensing information
  The information about the mass density of galaxy clusters provided by the
gravitational lens effect has inspired many inversion techniques. In this
article, updates to the previously introduced method in Grale are described,
and explored in a number of examples. The first looks into a different way of
incorporating time delay information, not requiring the unknown source
position. It is found that this avoids a possible bias that leads to
"over-focusing" the images, i.e. providing source position estimates that lie
in a considerably smaller region than the true positions. The second is
inspired by previous reconstructions of the cluster of galaxies MACS
J1149.6+2223, where a multiply-imaged background galaxy contained a supernova,
SN Refsdal, of which four additional images were produced by the presence of a
smaller cluster galaxy. The inversion for the cluster as a whole, was not able
to recover sufficient detail interior to this quad. We show how constraints on
such different scales, from the entire cluster to a single member galaxy, can
now be used, allowing such small scale substructures to be resolved. Finally,
the addition of weak lensing information to this method is investigated. While
this clearly helps recover the environment around the strong lensing region,
the mass sheet degeneracy may make a full strong and weak inversion difficult,
depending on the quality of the ellipticity information at hand. We encounter
ring-like structure at the boundary of the two regimes, argued to be the result
of combining strong and weak lensing constraints, possibly affected by
degeneracies.
