A Search for Fallback Disks in Four Young Supernova Remnants

We report on our search for the optical/infrared counterparts to the central compact objects in four young supernova remnants: Pup A, PKS 1209-52, RCW 103, and Cas A. The X-ray point sources in these supernova remnants are excellent targets for probing the existence of supernova fallback disks, since irradiation of a disk by a central X-ray source should lead to an infrared excess. We used ground-based optical and near-infrared imaging and Spitzer Space Telescope mid-infrared imaging to search for optical/infrared counterparts at the X-ray point source positions measured by the Chandra X-Ray Observatory. We did not detect any counterparts, and hence find no evidence for fallback disks around any of these sources. In PKS 1209-52, we are able to exclude a nearby optical/infrared candidate counterpart. In RCW 103, a blend of 3 faint stars at the X-ray source position prevents us from deriving useful limits. For the other targets, the upper limits on the infrared/X-ray flux ratio are as deep as (1.0--1.7)$\times 10^{-4}$. Comparing these limits to the ratio of $\approx 6\times10^{-5}$ measured for 4U 0142+61 (a young pulsar recently found with an X-ray irradiated dust disk), we conclude that the non-detection of any disks around young neutron stars studied here are consistent with their relatively low X-ray luminosities, although we note that a similar dust disk around the neutron star in Pup A should be detectable by deeper infrared observations.