An accurate strong lensing model of the Abell 2163 core
  Abell 2163 at $z \simeq 0.201$ is one of the most massive galaxy clusters
known, very likely in a post-merging phase. Data from several observational
windows suggest a complex mass structure with interacting subsystems, which
makes the reconstruction of a realistic merging scenario very difficult. A
missing key element in this sense is unveiling the cluster mass distribution at
high resolution. We perform such a reconstruction of the cluster inner total
mass through a strong lensing model based on new spectroscopic redshift
measurements. We use data from the Multi Unit Spectroscopic Explorer (MUSE) on
the Very Large Telescope (VLT) to confirm 12 multiple images of 4 sources with
redshift values from 1.16 to 2.72. We also discover four new multiple images
and identify 29 cluster members and 35 foreground and background sources. The
resulting galaxy member and image catalogs are used to build five cluster total
mass models. The fiducial model consists of 111 small-scale subhalos plus a
diffuse component, which is centered $\sim2$ arcseconds away from the BCG
belonging to the east Abell 2163 subcluster. We confirm that the latter is well
represented by a single, large-scale mass component. Its strong elongation
towards a second (west) subcluster confirms the existence of a preferential
axis, corresponding to the merging direction. From the fiducial model, we
extrapolate the cumulative projected total mass profile and measure a value of
$M(<300\,$kpc$) = 1.43^{+0.07}_{-0.06}\times 10^{14}\,$M$_{\odot}$, which has a
significantly reduced statistical error compared with previous estimates,
thanks to the inclusion of the spectroscopic redshifts. Our strong lensing
results are very accurate: the model-predicted positions of the multiple images
are, on average, only $0.15$ arcseconds away from the observed ones.
