The offset angle is sampled from a zero mean gaussian distribution with standard deviation 6 arcmin, and the model response is taken by scaling from the peak response of the sum of a large number of such randomly offset hexagonal responses. This value for sigma was that which gave the best fit to the scanning data from the Crab nebula. Relative PCU pointing The relative position of the center of each collimator field of view and the relative open area has been calibrated by scanning observations of the Crab nebula, and are summarized in table. The relative areas are normalized to PCU3, which has the largest throughput. The effective solid angle of the model is less than that of the triangular approximation.
Triangular approximation is shown for comparison.
Figure 2 illustrates the difference in the solid angle by plotting the differential solid angle as a function of radius for the two cases. The integration is done over the collimator model. This figure represents the sum of 5 collimator response, with offsets and relative areas as shown in the table. The linear approximation for the response, where is equal to , overestimates the solid angle. This compares with 0.000320578 from integrating this response numerically.