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Source variability can be studied with the WFC subject to the following
overall limitations:
- (i) Although each photon detected by the WFC is effectively time-tagged,
the instrument CDHS sets a minimum time resolution
ms. - (ii) Observations with any ROSAT instrument will typically
be interrupted every satellite orbit (see Chapter 7
). - (iii) The minimum time-scale for variability studies depends
on the source count rate. This is illustrated in
Figure 12.12 which shows the fractional intensity
change measurable (at 5
significance) as function of time
bin size for several different count rates. - (iv) The instrument deadtime has been calibrated and typically results
in a correction of
% to the on-time. - (v) The spacecraft wobble (cf. § 4.2.2 ) does not
cause any significant variations in the WFC count rate.
Michael Arida
Tue Jun 11 16:18:41 EDT 1996