XMM-Newton

Imaging Cameras - the EPIC Instrument

EPIC-MOS CCDs

Two of the EPIC cameras are equipped with MOS (Metal Oxide Semi-conductor) CCD arrays, pictured here. They are installed behind the X-ray telescopes that are equipped with the gratings of the Reflection Grating Spectrometers (RGS). (Image courtesy of Leicester University, University of Birmingham, CEA Service d'Astrophysique Saclay and ESA.)

EPIC P-N CCDs

One of the EPIC cameras uses pn CCDs - the CCDs are pictured here. (Image courtesy of MPI-semiconductor laboratory, MPE, Astronomisches Institut Tuebingen, Germany and ESA.)

The European Photon Imaging Camera (EPIC) is the main camera onboard XMM-Newton. It can perform both X-ray imaging and spectroscopy. It is actually three cameras in one, employing three different detectors to "see" X-rays.

The detectors are called "charge-coupled devices" or CCDs for short. They are similar to the detectors inside a common digital camera, but are sensitive to X-rays, not optical light. Two of the detectors are called "Metal Oxide Semiconductor" or MOS CCDs, and the other is called a p-n CCD. All three detectors can be used to create images of a target as well as take spectra.

The CCDs can also give a precise time when a given X-ray photon hits them. This allows astronomers to watch closely as astronomical targets vary in the number of X-rays they emit. That information can be used to determine some of the physical characteristics of the source. The main difference between the MOS detectors and the p-n detector, in fact, is in the time resolution. The MOS can distinguish between two X-ray photons falling on it in an interval of 1.5 milliseconds, while the p-n has a much better time resolution of 0.03 milliseconds, or 30 microseconds! As a trade-off, the MOS detectors have a higher spatial resolution: they can distinguish objects about a quarter the size that the p-n detector can.

The p-n CCD was built by the Max-Planck-Institut für extraterrestrische Physik (Garching) and the Astronomisches Institut Tübingen. It is made of a single wafer, a first for X-ray CCD astronomy technology. It is an array of electronic detectors, consisting of two rows of 6 chips with 64×200 pixels per chip.

The EPIC MOS detectors were put at the main focus of two of the three XMM telescopes (the third one being fitted with the EPIC p-n). Leicester University (UK), the University of Birmingham (UK), and CEN Service d'Astrophysique Saclay (France; the page is in French) participated in their construction. The are made up of 7 CCD chips of 600×600 pixels each, covering a field large enough to allow for the study of extended objects (like supernova remnants and clusters of galaxies).

EPIC-MOS camera  EPIC P-N camera

Left: The EPIC-MOS engineering and qualification model with its cooling radiator, in the cleanroom. (Copyright: Space Research Centre, University of Leicester)
Right: The EPIC PN camera in the cleanroom. (Credit: ESA)


A service of the High Energy Astrophysics Science Archive Research Center (HEASARC), Dr. Alan Smale (Director), within the Astrophysics Science Division (ASD) at NASA/GSFC