DISCOVERY OF A CANDIDATE OLD, ISOLATED NEUTRON-STAR IN THE FIELD OF A GALACTIC CIRRUS CLOUD

New x-ray, optical, and radio observations of the bright, unidentified x-ray source MS 0317.7-6647 are presented suggesting that this source is a likely compact stellar remnant. As part of the Einstein Extended Medium Sensitivity Survey, this source was discovered "serendipitously" in the Einstein Imaging Proportional Counter pointing towards the nearby (4.5 Mpc) spiral galaxy NGC 1313. The very high x-ray to optical flux ratio, pointlike ROSAT HRI detection, and extremely soft component in the x-ray spectrum of MS 0317.7-6647 eliminate all the usual classes of optical counterparts to faint x-ray sources except for a very massive x-ray binary (and black hole candidate) in NGC 1313, a nearby, companionless pulsar similar to Geminga, or a very nearby (∼100 pc) isolated, old neutron star slowly accreting interstellar matter onto its magnetic poles. The presence of an IR cirrus cloud which shadows the ∼1/4 keV x-ray background in this direction supports the latter possibility.