A Multiply-Imaged z $\sim$ 6.3 Lyman Alpha Emitter candidate behind
  Abell 2261
  While the Lyman-$\alpha$ ($\mathrm{Ly}\alpha$) emission line serves as an
important tool in the study of galaxies at $z\lesssim 6$, finding Ly$\alpha$
emitters (LAE) at significantly higher redshifts has been more challenging,
probably because of the increasing neutrality of the intergalactic medium above
$z\sim6$. Galaxies with extremely high rest-frame Ly$\alpha$ equivalent widths,
EW(Ly$\alpha$) $\gtrsim 150$ \AA{}, at $z>6$ are good candidates for Ly$\alpha$
follow-up observations, and can stand out in multiband imaging surveys because
of their unusual colors. We have conducted a photometric search for such
objects in the Cluster Lensing And Supernova survey with Hubble (CLASH), and
report here the identification of three likely gravitationally-lensed images of
a single LAE candidate at $z\sim6.3$, behind the galaxy cluster Abell 2261($z =
0.225$). In the process, we also measured with Keck/MOSFIRE the first
spectroscopic redshift of a multiply-imaged galaxy behind Abell 2261, at $z =
3.337$. This allows us to calibrate the lensing model, which in turn is used to
study the properties of the candidate LAE. Population III galaxy spectral
energy distribution (SED) model fits to the CLASH broadband photometry of the
possible LAE provide a slightly better fit than Population I/II models. The
best fitted model suggests intrinsic EW(Ly$\alpha$) $\approx 160$ \AA{} after
absorption in the interstellar and intergalactic medium. Future spectroscopic
observations will examine this prediction as well as shed more light on the
morphology of this object, which indicates it may be a merger of two smaller
galaxies.
