OLD ISOLATED ACCRETING NEUTRON-STARS - CONTRIBUTION TO THE SOFT-X-RAYBACKGROUND IN THE 0.5-2 KEV BAND

The issue of the observability of old isolated neutron stars (ONSs) ac creting from the interstellar gas is reconsidered using the spectra pr esented by Zampieri et al. In particular, we focus our attention on th e overall soft X-ray emission of ONSs, which may provide a substantial contribution to the X-ray background in the 0.5-2 keV band. It is fou nd that if accretion is channeled into polar caps by a magnetic field of similar to 10(9) G, up to similar to 12%-25% of the unresolved soft excess observed at high latitudes in the X-ray background can be expl ained in terms of emission from accreting isolated ONSs. However, this would imply the detection with ROSAT of similar to 10 sources deg(-2) above a threshold of similar to 10(-14) ergs cm(-2) s(-1). A brief re consideration of the observability of isolated ONSs as individual X-ra y sources is also presented.