XMM-Newton Users Handbook

4.5.2 Instrument and setup overheads

The following instrument and setup overheads apply to XMM-Newton science observations. Note that some of them will occur simultaneously, at the start of an observation.

• EPIC setup time is mainly due to the upload (in the case of the MOS cameras) or the calculation and download (in the case of the pn camera) of the offset tables needed to compute the amount of the optical loading of the CCD chips, i.e., the charges that must be subtracted to set the correct zero level for X-ray observations. The overhead of each pn exposure is mode dependent and varies from  0.5 to  1.5 hours. The overhead of each MOS exposure due to the offset table upload is about 10 minutes.

• The overhead of RGS exposures is about one minute and a half.

• The overheads of the OM exposures are mainly due to the setup of the instrument and the field acquisition driven by the guide star recognition (cp. § 3.5.7).

Instrument and setup overheads need to be taken into account in XMM-Newton observing proposals. A detailed description of the instrument and setup overheads can be found in the XRPS Users' Manual (XRPS).