XMM-Newton Users Handbook

3.5.3.2 OM default configurations

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 (§ 3.5.3.1). 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 default configurations are as follows:

Figure 100: Setup of OM imaging mode default mode observations consisting of a sequence of 5 exposures. The science windows are indicated by solid lines, the detector windows by dashed lines. A 16 in-memory pixel margin around the science window is allocated to accommodate spacecraft drifts.

1. Imaging Mode default (named EPIC/RGS Image in the RPS, depending on the prime X-ray instrument)
   • A setup of 5 consecutive exposures per filter, covering 92% of the total (17'$\times$17') OM FOV. Each exposure having 2 windows.

   • In each of the 5 exposures per filter a large fraction of the FOV will be covered by one large window , while the central 2'$\times$2' high resolution imaging mode window is observed in all the exposures. The continuous exposure of the central window, ensures continuous monitoring of the prime target (at the centre of the FOV; see Fig. 100).

   • The central window has high spatial resolution (0".5$\times$0".5) while the lateral windows have 2$\times$2 in-memory pixel binning (1''.0 pixels)

   An example of the configuration corresponding to this mode is shown in Fig 101.

   Figure 101: Example of a field imaged with the default Image Mode configuration.

   

2. Fast Mode default (named EPIC/RGS Image Fast in the Remote Proposal System, RPS, depending on the prime X-ray instrument)
   • Image windows configuration as under 1 (i.e. Image Mode default windows).

   • An additional central window is operated in the OM Fast mode. Its size is 22$\times$23 in-memory pixels (10''.5$\times$10''.5). It is responsibility of the PI to carefully check the accuracy of the target coordinates, to avoid substantial flux losses.

3. Full-Frame imaging modes (Full Frame High/Low Resolution in the RPS)

   It is possible to obtain images of the whole OM field of view in full (high) or 2$\times$2 binned (low) resolution. These modes do not allow tracking, and have higher instrumental overheads than the 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 § 3.5.7), 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).

4. Default grism configurations

   Two standard configurations are available for OM optical or UV grisms:

   • a predefined default window, which will contain the spectrum of the target (with its 0th order) at full detector resolution (Science User Defined mode in RPS)

   • a Full Frame Low Resolution exposure, which provides the spectra of all the targets in the OM FOV, with slightly degraded spatial (and hence spectral) resolution (Full Frame Low Resolution mode in RPS)

In addition to these default configurations it is also possible to define customised windows using the Science User Defined mode (see § 3.5.10.1).

Apart from the configuration of the OM exposures, exposure times and filters have to be specified.