SciSim is a collection of programmes that can model XMM observations. Rays can be generated using a random generator and injected into the XMM telescope optics. Although all XMM instruments normally operate simultaneously, each can be excluded from SciSim model runs for the sole purpose of cutting back on processing time.
The individual SciSim components model one part of XMM each. Starting with the cosmic simulator (CSim), including the ray generator, which produces the input radiation (Appendix A.3.1), the propagation of the incoming radiation through the different parts of XMM is modeled, first through the mirrors (Appendix A.3.2) and then either directly onto the EPIC pn camera or onto the RGAs (Appendix A.3.4) and then on to either the EPIC MOS cameras (Appendix A.3.3) in the prime focus or the RFCs in the secondaries of two out of three XMM telescopes (Appendix A.3.4). Two examples of SciSim runs are presented in Appendix A.5.
SciSim has been programmed to resemble XMM as closely as possible. However, it is not a complete tool, because some quantities like, e.g., the relative alignment of the different science instruments with respect to each other is not yet known. Missing items are listed in Appendix A.6. Since SciSim produces output files in the ODF format and the SAS (which is the software package to process such ODFs) is still under development, the SciSim to SAS interface is not yet fully developed. During this time, the SciSim tools presented in Appendix A.4 can be used to convert SciSim output to formats that can be read by other software packages.