The `Cosmic Seagull': a highly magnified disk-like galaxy at z~2.8
  behind the Bullet Cluster
  We present Atacama Large Millimeter/submillimeter Array measurements of the
`Cosmic Seagull', a strongly magnified galaxy at z=2.7779 behind the Bullet
Cluster. We report CO(3-2) and continuum 344~$\mu$m (rest-frame) data at one of
the highest differential magnifications ever recorded at submillimeter
wavelengths ($\mu$ up to ~50), facilitating a characterization of the
kinematics of a rotational curve in great detail (at ~620 pc resolution in the
source plane). We find no evidence for a decreasing rotation curve, from which
we derive a dynamical mass of ($6.3\pm0.7)\times10^{10} M_{\odot}$ within $r =
2.6\pm0.1$ kpc. The discovery of a third, unpredicted, image provides key
information for a future improvement of the lensing modeling of the Bullet
Cluster and allows a measure of the stellar mass,
$1.6^{+1.9}_{-0.86}\times10^{10} M_{\odot}$, unaffected by strong differential
magnification. The baryonic mass is is expected to be dominated by the
molecular gas content ($f_{gas} \leq 80 \pm 20$ \%) based on an $M_{H_2}$ mass
estimated from the difference between dynamical and stellar masses. The star
formation rate is estimated via the spectral energy distribution ($SFR = 190
\pm 10 M_{\odot}/yr$), implying a molecular gas depletion time of $0.25\pm0.08$
Gyr.
