Search for an Near-IR Counterpart to the Cas A X-ray Point Source

We report deep near-infrared and optical observations of the X-ray point source in the Cassiopeia A supernova remnant, CXO J232327.9+584842. We have identified a $J=21.4 \pm 0.3$ mag and $K_{s}=20.5 \pm 0.3$ mag source within the 1-$\sigma$ error circle, but we believe this source is a foreground Pop II star with $T_{\rm eff}=2600$-2800 K at a distance of $\approx 2$ kpc, which could not be the X-ray point source. We do not detect any sources in this direction at the distance of Cas A, and therefore place 3-$\sigma$ limits of $R \gsim 25$ mag, ${\rm F675W} \gsim 27.3$ mag, $J\gsim 22.5$ mag and $K_{s} \gsim 21.2$ mag (and roughly $H \gsim 20$ mag) on emission from the X-ray point source, corresponding to $M_{R} \gsim 8.2$ mag, $M_{\rm F675W} \gsim 10.7$ mag, $M_{J} \gsim 8.5$ mag, $M_{H} \gsim 6.5$ mag, and $M_{K_{s}} \gsim 8.0$ mag, assuming a distance of 3.4 kpc and an extinction $A_{V}=5$ mag.