A Parsec-scale Bipolar H$_2$ Outflow in the Massive Star Forming
  Infrared Dark Cloud Core MSXDC G053.11+00.05 MM1
  We present a parsec-scale molecular hydrogen (H$_2$ 1-0 S(1) at 2.12~\micron)
outflow discovered from the UKIRT Widefield Infrared Survey for H$_2$. The
outflow is located in the infrared dark cloud core MSXDC G053.11+00.05 MM1 at
1.7 kpc and likely associated with two young stellar objects (YSOs) at the
center. The overall morphology of the outflow is bipolar along the NE-SW
direction with a brighter lobe to the southwest, but the detailed structure
consists of several flows and knots. With the total length of $\sim$1 pc, the
outflow luminosity is fairly high with $L_{\rm H_{2}} > 6~L_{\sun}$, implying a
massive outflow-driving YSO if the entire outflow is driven by a single source.
The two putative driving sources, located at the outflow center, show
photometric variability of $\gtrsim$1 mag in {\it H}- and {\it K}-bands. This,
with their early evolutionary stage from spectral energy distribution (SED)
fitting, indicates that both are capable of ejecting outflows and may be
eruptive variable YSOs. The YSO masses inferred from SED fitting are
$\sim$10~$M_{\sun}$ and $\sim$5~$M_{\sun}$, suggesting the association of the
outflow with massive YSOs. The geometrical morphology of the outflow is well
explained by the lower mass YSO by assuming a single source origin, but without
kinematic information, the contribution from the higher mass YSO cannot be
ruled out. Considering star formation process by fragmentation of a high-mass
core into several lower mass stars, we also suggest the possible presence of
another, yet-undetected driving source deeply embedded in the core.
