A Recipe for Pile-up Mitigation?
These simulation results, while illustrative of the concept of masking to improve piled-up spectra, do not provide a recipe for pile-up mitigation that can be blindly followed. Pile-up effects clearly depend on the incident spectrum, and no astrophysical spectrum looks like the lines we've simulated. Furthermore, the quality metric we've used is not defined for a polychromatic spectrum.

Nevertheless, an observer could use these results either to estimate the masking a proposed observation will require or to roughly clean up an actual observation. Assuming a point source on axis, the steps would be:

• From the observed event list, measure either the raw event rate, the g02346 event rate, or the raw event rate outside of a  1" circle centered on the source. These quantities all serve as proxies for the incident photon flux, which is unknown.
• Using curves similar to those in Figure 6.45 find the O, Al, & Cu simulations that produced the same flux proxy value.
• For O, Al, & Cu, look up the exclusion radius that achieves the desired quality level.
• Use the largest of those radii to filter the events (i.e. assume all photons from the source are at the ``worst'' of the three energies).
• Adjust the AXAF effective area curve by the relative efficiency shown in Figure 6.43-right. Obviously one would want to compute the relative efficiency more accurately and at more energies than was done here.

Figure 6.45: Flux proxies for seven simulations