New Multiply-Lensed Galaxies Identified in ACS/NIC3 Observations of
  Cl0024+1654 Using an Improved Mass Model
  We present an improved strong-lensing analysis of Cl0024+1654 ($z$=0.39)
using deep HST/ACS/NIC3 images, based on 33 multiply-lensed images of 11
background galaxies. These are found with a model that assumes mass
approximately traces light, with a low order expansion to allow for flexibility
on large scales. The model is constrained initially by the well known 5-image
system ($z$=1.675) and refined as new multiply-lensed systems are identified
using the model. Photometric redshifts of these new systems are then used to
constrain better the mass profile by adopting the standard cosmological
relation between redshift and lensing distance. Our model requires only 6 free
parameters to describe well all positional and redshift data. The resulting
inner mass profile has a slope of $d\log M/d\log r\simeq -0.55$, consistent
with new weak-lensing measurements where the data overlap, at $r\simeq200$
kpc/$h_{70}$. The combined profile is well fitted by a high concentration NFW
mass profile, $C_{\rm vir}\sim 8.6\pm1.6$, similar to other well studied
clusters, but larger than predicted with standard $\Lambda$CDM. A well defined
radial critical curve is generated by the model and is clearly observed at $r
\simeq 12\arcsec$, outlined by elongated images pointing towards the centre of
mass. The relative fluxes of the multiply-lensed images are found to agree well
with the modelled magnifications, providing an independent consistency check.
