There are three scientific instruments aboard XMM-Newton:
European Photon Imaging Camera (EPIC)
At the prime focus of each of the spacecraft's three telescopes, behind a six-position filter wheel, is a European Photon Imaging Camera (EPIC). With silicon chips that can register extremely weak X-ray radiation, these advanced Charge-Coupled Device cameras (CCD) are capable of detecting rapid variations in intensity, down to a thousandth of a second and less!
Reflection Grating Spectrometer (RGS)
For a complementary analysis of the spectrum, two of the three telescopes have a grating structure on their mirror module that reflects about 40 per cent of the incoming rays to a secondary focus, with its own CCD camera. This Reflection Grating Spectrometer (RGS) "fans out" the various wavelengths, thus indicating, in more detail than EPIC, the exact condition of individual elements, such as oxygen and iron.
Optical Monitor (OM)
The third instrument aboard XMM-Newton is a conventional but very sensitive optical/UV telescope, the Optical Monitor (OM). It can observe simultaneously the same regions as the X-ray telescopes, but at ultraviolet and visible wavelengths. This gives astronomers complementary data about the X-ray sources. The 2-metre long telescope is mounted on the mirror support platform of XMM-Newton alongside the X-ray mirror modules. In orbit, this 30 cm diameter telescope is as sensitive as a four-metre diameter instrument on the Earth's surface.