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Jim Chiang (11/29/06)--With regard to handling pointed observations, generalizing the Psf integrals to include a time-dependent zenith angle cut may turn out to be computationally intractable. As an alternative, Julie suggested making a cut on acceptance as a function of inclination angle wrt to the instrument z-axis. This would be straight-forward to implement in the exposure calculations, except that the cuts on the events would be applied to the measured inclinations, whereas our IRFs are defined as a function of trueinclination. An alternative that would not make this sort of approximation can actually be applied within the current set of ScienceTools: Define a set of GTIs such that the instrument z-axis is within a specified angle (say 115 degrees) of the spacecraft zenith. For pointed mode, this will likely decrease the on-source exposure time substantially, but this is a procedure that can be applied now.
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