As with EPIC and RGS datasets, many files are associated with an OM dataset. The INDEX.HTM file, and links therein, are viewable with a web browser and will help you navigate the dataset. The different types of files are discussed in Chapter 5.2; however, since the OM is somewhat different from the other instruments on-board XMM-Newton, we will discuss them in more detail in later sections.
The OM can operate in IMAGING, FAST, and GRISM mode. Each of these modes has dedicated commands to reprocess the data: omichain, omfchain, and omgchain. These are Perl scripts which each call several procedures sequentially that are used to prepare the data for processing, make and apply flatfield images, and detect sources. The tasks omichain and omfchain also calculate the instrumental magnitudes of sources, find the position of the sources (in equatorial coordinates), and produce a sky image; omgchain produces a spectrum. If you run these chains, it is helpful to inspect the sas_log file to get a detailed list of the performed tasks. These chains rely on filters specified by the user; if no arguments are given, they run on all the files present in the ODF directory. Due to the long file names and the large number of input parameters, users are urged to simply use the chains and not run the chains' individual tasks one at a time.
Most OM data are obtained in IMAGING mode. If they were obtained in the FAST mode, there will be an additional event list file corresponding to the Fast window (*FAE.FIT). Reprocessing of data taken in FAST mode is discussed in §9.4. Reprocessing OM GRISM data is discussed in §9.5.
As always, it is strongly recommended that you keep all reprocessed data in its own directory! Hera places output files in whichever directory it is in when a task is called. Throughout this primer, it is assumed that the Pipleline Processed data in the PPS directory, the ODF data (with upper case file names, and uncompressed) are in the directory ODF, and the analysis is taking place in the PROC directory.
At this point, it is assumed that you have downloaded the data from the HEASARC archive onto a Hera server, standard or anonymous Hera is running (see §4.2), and you have prepared the data for processing (see Chapter 6). We will use the example data as noted in Table 6.1, though any dataset with the appropriate mode will suffice.