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The general points discussed above for the XRT survey are also applicable to the WFC.
The WFC field of view is in diameter. During the survey, the S1 and S2 filters will be used alternately, hence providing two XUV colours in the waveband from about 60 up to 200 Å (see Table 5.3).
During the survey a source will be scanned for up to about a minute every 1.5 hours (one satellite orbit), over a interval of days, where is the ecliptic latitude of the source. The total exposure time at most locations on the sky should thus be s (after allowing for a loss of about 25 percent due to high background regions). The available time is divided approximately equally between the two survey filters, which are alternated at a frequency of approximately once per day. As the WFC and XRT are coaligned and are operated for essentially the same time intervals, the anticipated WFC survey exposure for any point in the sky can be determined by reference to Figure 6.1 which shows the XRT survey exposure. In order to get the WFC survey exposure in either of the survey filters, the exposures given in Figure 6.1 should be multiplied by a factor of 3 (because of the larger field of view of the WFC).
The spatial resolution of the WFC is about 1.4' FWHM (full width at half maximum) within about of the optical axis, and for the survey it is about 2.5' FWHM averaged over the field-of-view. The location accuracy (error circle 90% confidence radius) for point sources in the survey varies from for the weakest ones (set by photon counting statistics) to for strong sources (limited by the WFC attitude determination and systematic errors - some improvement on this may be expected eventually).