The Highest L_x/L_opt Sources in the ROSAT All-Sky Survey

Theoretical predictions for the number of INSs in the ROSAT AllSky Survey,>10^2, dwarf the group of seven identified to date, at least partly becausesource confusion in the PSPC error circles has made counterpart identification/exclusion difficult. We have developed a novel statistical technique to quantifywhich RASS sources are least likely to be represented by a counterpart in thelatest optical or radio source catalogs. Short XMM observations of these sourceswill provide us with arcsecond positions to confirm the absence of brightcounterparts and enable followup observations, and give us >1000count Xrayspectra which may suggest the source nature. By this means we hope to discovernew INSs in bulk and, potentially, other high Lx/Lopt source classes as well. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]