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A series of pointed observations and a five-day mini-survey were made over a roughly six-week period prior to the start of the all-sky survey. The purpose of these observations was instrument calibration and performance verification, including checking out S/C systems, turn-on of both XRT and the WFC focal plane detectors, boresighting, spectral and spatial calibration, and background measurements. Whilst many standard X-ray calibration sources were observed, this phase also included some targets from the approved AO-1 program selected to provide a range of scientific objectives. A summary list of these PVC observations is contained in App. B The calibration observations are described in more detail in Chap. 7.
Figure 1.3: An Aitoff projection of the celestial sphere showing the (logarithmic) exposure time of the ROSAT all-sky survey. The spring equinox is located at the centre, with increasing RA plotted to the left. The lowest contour indicates a PSPC total exposure of 250 s, with each additional contour representing an increase by a factor 2. The rough WFC exposure time in each survey filter can be obtained by multiplying these values by a factor 3 (due to the larger field of view of the WFC)
[ROSAT AO-21991, NRA 91-OSSA-31991].