To ease the use of the OM and to maximise the scientific yield of observations in cases when no particular instrument configuration is requested, OM default configurations have been defined. There is one type of default configuration per OM observing mode, thus one for the imaging mode and one for the Image plus Fast mode (§ 18.104.22.168). Default windows have also been predefined for the V and UV grisms exposures. Moreover, two additional full frame modes are available which allow imaging observation of the whole OM field of view.
The possible configurations are as follows:
Up to five windows (two of them in Fast mode) covering different areas of the detector can be defined (see Sect. 22.214.171.124).
It is possible to obtain images of the whole OM field of view in full (high) or 22 binned (low) resolution. These modes do not allow tracking (see § 3.5.4), and have higher instrumental overheads than the Modes using windows, either User Defined windows or Imaging Mode default. However, they allow homogeneous sampling of the whole OM field of view. They are therefore particularly well suited for survey studies or to obtain multiobject grism spectroscopy in a wide field. These modes have a single window, no other window can be defined (either in image or Fast mode) within the same exposure. Along an observation, Full-Frame imaging modes can be combined with modes using windows that require Field Acquisition (FAQ, see § 3.5.8), particularly Fast mode windows. In this case the Full-Frame exposures must be performed after all the exposures which need FAQ, because Full-Frame modes nullify the results of FAQ.
The lack of tracking in Full Frame mode does not affect the quality of the image because, as experience has shown us, the drift of the XMM-Newton spacecraft is almost negligible (less than one arc sec per hour).
Two standard configurations are available for OM optical or UV grisms:
Examples of the Imaging and Fast default modes are shown in Figs. 110 and 111.
Apart from the configuration of the OM exposures, exposure times and
filters have to be specified.
The described Default configurations for Imaging and Fast modes provide a
very simple and easy to use set-up aimed at obtaining a good coverage of the
main target located at the boresight and imaging at the same time the complete
field of view (92% with 5 consecutive exposures).
However, due to the limitations imposed by the coincidence losses in the detector these Default configurations are not recommended in case of bright sources and in variability studies. As explained in section 3.5.5, the coincidence losses (and their correction) depend on the frametime. The different detector windows defined for the five exposures of the Default configuration may have very different frametimes leading, for high count rates, to very large and inhomogeneous corrections and errors. It is better in these cases to select a unique window using Science User Defined mode.