Visual inspection of each dataset can be time-consuming, since sequences can have dozens of significant sources. For example, many sequences contain large extended X-ray sources (like supernovae remnants or emission from clusters of galaxies) which can confuse the source detection algorithm resulting in large numbers of spurious detections, all of which must be flagged.
In order to minimize the amount of time spent in visual inspection, software tools have been written which allow easy access to the derived source characteristics and the X-ray images. These GUI-based tools allow the screener to select data sets and sources, overplot sources on X-ray images of the field, and view and set quality flags. There are 2 software tools currently in use, one for the PSPC data and one for the HRI.
The operating goal of these systems was to facilitate examination of details of source and field characteristics and to allow the operator to perform the evaluation and flag setting in 10 minutes per field (or less). The checker examines different images of the observation with the sources marked by color coded circles (PSPC) or boxes (HRI). The size of the circle is matched to the (off-axis) size of the PRF and the size of the box corresponds to the size of the detect cell. The colors indicate the flagging condition imposed by the automatic phase of the operation (e.g. sources below the S/N threshold are blue, sources for which all flags are still false are green, etc).
The operator then flags suspected parameters on a source by source basis. One of the most common flags set is the 'm' flag: multiple detections of a single source. This flag is applied to the many detections which often occur in the wings of the PRF of a very bright source (HRI) and to the large number of detections associated with extended sources such as clusters of galaxies or super nova remnants. When the operator clicks on the 'm' flag, the software also changes 'f' to true, although we almost always leave the single detection which best describes the actual source with 'f' = 'false'. Note that 'multiple detections' is not used for the HRI case of different detect cell sizes.