  We present new HST/WFC3 imaging data of RCSGA 032727-132609, a bright lensed
galaxy at z=1.7 that is magnified and stretched by the lensing cluster RCS2
032727-132623. Using this new high-resolution imaging, we modify our previous
lens model (which was based on ground-based data) to fully understand the
lensing geometry, and use it to reconstruct the lensed galaxy in the source
plane. This giant arc represents a unique opportunity to peer into 100-pc scale
structures in a high-redshift galaxy. This new source reconstruction will be
crucial for a future analysis of the spatially-resolved rest-UV and
rest-optical spectra of the brightest parts of the arc.
