XRCF Measurements of ACIS/HRMA PSF

Each XRCF Phase H PSF observation consists of photon-counting-mode data from an approximately monochromatic source. The FAM was positioned so that the bulk of the PSF is contained within the boundaries of one ACIS amplifier, so that most PSF photons have the same gain. The system was fully cooled and focused before PSF measurements were made. The PSF was measured at several energies, both on-axis and at several off-axis locations (thus the PSF dataset involves all ACIS CCDs). The inner core of the PSF was sampled using a low flux rate (the ``PI'' tests); separate tests were made to populate the PSF wings (the ``PW'' tests) in a reasonable amount of time by increasing the flux. These PW tests sacrifice information about the PSF core due to heavy pile-up.

It is useful to note that other XRCF tests can be used in PSF analysis; the count rate linearity tests and some focusing measurements also serve as PSF samples. In fact, the lowest-flux count rate linearity tests represent the best available PSF-core measurements, as they suffer the least pile-up of the entire dataset. A summary of all XRCF PSF data is presented in Section 6.1.4.