The European Photon Imaging Camera on XMM-Newton: The MOS cameras

The EPIC focal plane imaging spectrometers on XMM-Newton use CCDs to record the images and spectra of celestial X-ray sources focused by the three X-r ay mirrors. There is one camera at the focus of each mirror; two of the cam eras contain seven MOS CCDs, while the third uses twelve PN CCDs, defining a circular field of view of 30' diameter in each case. The CCDs were specia lly developed for EPIC, and combine high quality; imaging with spectral res olution close to the Fano limit. A filter wheel carrying three kinds of X-r ay transparent light blocking filter, a fully closed, and a fully open posi tion, is fitted to each EPIC instrument. The CCDs are cooled passively and are under full closed loop thermal control. A radio-active source is fitted for internal calibration. Data are processed on-board to sate telemetry by removing cosmic ray tracks, and generating X-ray event files; a variety of different instrument modes are available to increase the dynamic range of the instrument and to enable fast timing. The instruments were calibrated u sing laboratory X-ra;rr beams, and synchrotron generated monochromatic X-ra y beams before launch; in-orbit calibration makes use of a variety of celes tial X-ray; targets. The current calibration is better than 10% over the en tire energy range of 0.2 to 10 keV. All three instruments survived launch a nd are performing nominally in orbit. In particular full field-of-view cove rage is available, all electronic modes work, and the energy resolution is close to pre-launch values. Radiation damage is well within pre-launch pred ictions and does not yet impact on the energy resolution. The scientific re sults from EPIC amply fulfil pre-launch expectations.