Search for a Near‐Infrared Counterpart to the Cassiopeia A X‐Ray Point Source

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Abstract
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 ± 0.3 mag and a Ks = 20.5 ± 0.3 mag source within the 1 σ error circle, but we believe this source is a foreground Population II star with Teff = 2600-2800 K at a distance of ≈2 kpc that 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 σ limits of R 25 mag, F675W 27.3 mag, J 22.5 mag, and Ks 21.2 mag (and roughly H 20 mag) on emission from the X-ray point source, corresponding to MR 8.2 mag, MF675W 10.7 mag, MJ 8.5 mag, MH 6.5 mag, and M 8.0 mag, assuming a distance of 3.4 kpc and an extinction of AV = 5 mag.

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