A highly magnified gravitationally lensed red quasar at z = 2.5 with
  significant flux anomaly: Uncovering a missing population
  We present the discovery of a gravitationally lensed dust-reddened QSO at
$z=2.517$ discovered in a survey for red QSOs by infrared selection.
$Hubble~Space~Telescope$ imaging in the WFC3/IR F160W and F125W filters reveals
a quadruply lensed system in a cusp configuration. We find that compared to the
central image of the cusp, the nearby, brightest image is anomalous by a factor
of $\sim7-11$. Although the source is extremely bright in the mid-infrared, a
magnification by a factor of $\sim50-120$ places an upper limit of 1.35 mJy on
the intrinsic mid-infrared brightness, well below the $WISE~W4$ detection limit
of 6 mJy. We find that this QSO is moderately reddened, with $E(B-V)=0.7$ and
that $\sim1\%$ of the intrinsic spectrum is leaked back into the line of sight
resulting in an upturn in its UV spectrum. We conclude that the QSO's reddening
is intrinsic and not due to the lens. Consistent with previous red quasar
samples, this source exhibits outflows in its spectrum as well as morphological
properties suggestive of it being in a merger-driven transitional phase.
Depending on how $L_{\rm bol}$ is computed, the quasar's accretion rate may be
as high as $0.26~L_{\rm Edd}$. We detect two Lyman limit systems, at $z=2.102$
and $z=2.431$, with absorption by metal lines likely at small impact parameter
to the QSO, and a putative lens redshift of $z=0.599$. Given the rarity of quad
lenses, the discovery of this source allows detailed study of a less luminous,
more typical infrared-selected quasar at high redshift.
