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The expected (50% in detect cell) count rate from a source with a blackbody spectrum (perhaps a neutron star) needs to be estimated. The source has L ergs s in the ROSAT\ energy band (0.1 to 2.4 keV), and is at a distance of 2 kpc with N cm (log(N ). The assumed temperature is equivalent to 0.1 keV. The unabsorbed flux for this source is ergs cm s , or in units of the flux is . From the Table 11.5 or Figure 11.7 the appropriate ECF is , and the expected count rate is counts s . We estimate that a detection of this source at the level will require an observation time of about 4,000 seconds.