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3.3.1 Blackbody spectrum example

The expected count rate from a source with a blackbody spectrum (perhaps a neutron star) needs to be estimated. The source has L x = 1033 ergs s-1 in the ROSAT energy band (0.1 to 2.4 keV), and is at a distance of 2 kpc with N H = 1 x 1021 cm-2(log(N H) = 21). The assumed temperature is equivalent to 0.1 keV. The unabsorbed flux for this source is FS, 0 = 2.09 x 10-12 ergs cm-2 s-1. From Table 11 or Figure 33, the appropriate ECF is 5.63 x 109, and the expected count rate is 0.012 ct s-1. We estimate that a detection of this source at the 5$ \sigma$ level will require an observation time of about 4,000 seconds.