The XMM-ESAS package produces a fairly large number of intermediate files during the processing of an observation data set. Many shouldn't be touched while the processing is in progress. In the following, we will indicate whether output files are diagnostic (thus disposable), an intermediate step, or final output, in order to make it more clear what needs to be protected and what can be overwritten. However, as discussed below, if spectra are required from multiple regions of the same exposure, the final products (e.g., spectral files, RMFs, and ARFs) must be renamed or (better yet) moved before processing another region. The example scripts in Appendix B demonstrate a simple way of keeping track of everything. Similarly, some files will not change, so they should be retained in order to speed processing.
Among the developers there has been a great deal of discussion about file names and trying to get them to fit the SAS model. Unlike most SAS tasks, some ESAS tasks require multiple (sometimes an indefinite number) of input files and produce a prodigious number of output files. In previous versions of ESAS, input file names were partially hard-wired. The new ESAS tasks have been restructured so that, with some exceptions, the input and output filenames can be either user determined or constructed by the routine itself.