Limitations

Our ability to reproduce the data is limited by several factors, many of which will soon be ameliorated. The current SAOSAC rays for XRCF ACIS data presume that the source is at a finite distance, but to achieve the best possible simulated results they also need to account for the finite size of the source (the rays currently assume a point-like source). These improved rays should be available soon. The SAOSAC rays are also monochromatic, whereas the sources are not. This is probably not a major concern for the PSF simulations at present. As mentioned above, our strongest current limitation is the inability to adjust the source flux. We anticipate that the next version of MARX will relieve this constraint. The acis_sim program also has a long list of planned revisions (see Section 7.1), some of which may affect the simulated PSF. The most critical change to be made in the transition from XRCF data to on-orbit predictions is the inclusion of aspect errors. Existing simulator components give us the ability to randomize photon positions by a given amount, but no more detailed prescription of aspect errors has been attempted.