CIAO 2.0.2 Release Notes

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We have discovered two bugs in the asp_apply_sim program. asp_apply_sim is used to add the SIM boresight offsets derived from fiducial light monitoring to the aspect offsets; it is used only as preparation for the asphist program (for other applications we keep the two sets of offsets separate, retaining information on the off-axis angles; strictly the vignetting should be applied to the aspect offsets only and the instrument qe map should be applied to the combination, but the error is very small).

The bugs are:

• the SIM offsets are being applied with the wrong sign
• they are being rotated through only the roll *offset* instead of through the total roll.

Hence, the magnitude of this bug depends on both the size of the sim offsets (typically around 10 pixels) and the roll angle.

CIAO 2.0.2 includes a fixed version of asp_apply_sim. If structure at the few pixel scale in your exposure maps is critical to your analysis, you should consider remaking the exposure maps. The event files are fine, since they do the full calculation treating aspect and fiducial SIM offsets separately.