XMM RPS Users' Manual

   
Planning an XMM observation

Many trade-offs in the analysis of data may be made at leisure on the ground, subject to availability of suitable tools and calibration knowledge (see, e.g., the UHB sections on EPIC pile-up and points of concern ). At the present stage, PIs must be aware only of those issues which irretrievably corrupt the data taken in-orbit and transmitted to ground and plan & prepare their observations accordingly. Corruption of data can, e.g., take the form of:

• Confusion or mixing of the source photons with those from another source in or near the field of view,

• corruption of the reported energy data due to piling up of more than one photon per pixel per CCD readout frame or to excessive optical loading of the X-ray CCDs,

• loss of data due to pile-up effects, or due to saturation of telemetry rates,

• loss of calibration accuracy due to photons lost at CCD chip edges.

Generally to appreciate these issues, the observer needs only to consider the target of interest from the point of view of a simple matrix of properties, namely if the source is bright or faint, if one is interested primarily in spatial, spectral or temporal information and whether the target is extended or point-like.

For each type of XMM instrument (EPIC, RGS, OM) the user must then consider the optimal choice of instrument setup to maximise the scientific return of the observation. General preparatory steps to be taken are:

1.

As a minimum calculate the expected count rates using the information contained in the UHB or the PIMMS (Portable Interactive Multi-Mission Simulator) software from the Goddard Space Flight Center, at the URL
http://heasarc.gsfc.nasa.gov/Tools/w3pimms.html,

2.

using the catalogue interface of SciSim and other catalogues, determine the brightest optical object in the field of view; if any source beyond the OM brightness limit should be in its field of view (FOV), the OM must be pt in the ``GO-off'' mode;

3.

using the catalogue interface of SciSim and other catalogues, determine the presence of nearby X-ray bright objects which may cause straylight degradation and

4.

using the XMM Target Visibility Tool, determine the maximum duration of continuous visibility available in any orbit.

If the planned observations depend very critically on one of the above parameters and the level of accuracy provided by the existing XMM online documentation is not sufficient to show whether the observations would be feasible, observers should consider performing a detailed simulation with the XMM Science Simulator (SciSim) to ray-trace the whole observation, and analyse the data in an appropriate manner (e.g., with XSPEC). SciSim is available via the URL http://astro.estec.esa.nl/XMM/scisim/scisim.html.

We will now describe - in the form of checklists - which aspects of an XMM observation must be considered when planning an observation for different kinds of targets. § A (below) contains examples for the possible choices for some crucial input parameters, depending on the target properties. An example for how to prepare filling in the XRPS form sheets based on such considerations and parameter choices is presented in § 3.2.