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The Concept of Threshold

It was realized that in practice it would be nearly impossible to judge the reliability of detections which were just above the thresholds used in the SASS processing. Therefore we devised the 'n' flag which, if TRUE, means that the detection was not examined during visual inspection. For the HRI, only sources with S/N > 4 were examined, for the PSPC a likelihood of > 14 is required. Detections with values below these limits will still be in the RRA , but marked with a not-checked flag: many of these are real sources.
Wed Jun 3 11:20:57 EDT 1998