Hubble Frontier Fields: Predictions for the Return of SN Refsdal with
  the MUSE and GMOS Spectrographs
  We present a high-precision mass model of the galaxy cluster
MACSJ1149.6+2223, based on a strong-gravitational-lensing analysis of Hubble
Space Telescope Frontier Fields (HFF) imaging data and spectroscopic follow-up
with Gemini/GMOS and VLT/MUSE. Our model includes 12 new multiply imaged
galaxies, bringing the total to 22, comprised of 65 individual lensed images.
Unlike the first two HFF clusters, Abell 2744 and MACSJ0416.1-2403, MACSJ1149
does not reveal as many multiple images in the HFF data. Using the Lenstool
software package and the new sets of multiple images, we model the cluster with
several cluster-scale dark-matter halos and additional galaxy-scale halos for
the cluster members. Consistent with previous analyses, we find the system to
be complex, composed of five cluster-scale halos. Their spatial distribution
and lower mass, however, makes MACSJ1149 a less powerful lens. Our best-fit
model predicts image positions with an RMS of 0.91". We measure the total
projected mass inside a 200~kpc aperture as ($1.840\pm 0.006$)$\times
10^{14}$M$_{\odot}$, thus reaching again 1% precision, following our previous
HFF analyses of MACSJ0416.1-2403 and Abell 2744. In light of the discovery of
the first resolved quadruply lensed supernova, SN Refsdal, in one of the
multiply imaged galaxies identified in MACSJ1149, we use our revised mass model
to investigate the time delays and predict the rise of the next image between
November 2015 and January 2016.
