XMM Users' Handbook

   
Special science exposures

Optimal scientific usage of the XMM instruments sometimes requires special (science) exposures. These are not overheads and therefore part of the requested science observing time:

• RGS spectroscopy mode data to be taken before or after high time resolution mode observations in order to identify the location of the incident spectrum on the CCD array (and thus the timing of the readouts) very accurately.

• An OM image should be acquired before every grism exposure.

• OM fast mode images should be embedded in an image mode science window. This will help with the fixed pattern noise correction, as it provides a template at the proper count rate level.