ESA Science & Technology14-Jul-2005 05:56:33



The name of XMM-Newton stems from the design of its mirrors, a masterpiece of engineering, the highly nested X-ray Multiple Mirrors. These are enabling astronomers to discover more X-ray sources than with any of the previous space observatories. In one day, XMM-Newton will see more sources in a small region of sky than one of the earliest X-ray satellites, UHURU, found across the whole sky during its three years in operation. But the programme also has a more formal name: the High-Throughput X-ray Spectroscopy Mission. Spectroscopy, the spreading of light into a spectrum, allows astronomers to measure a source's composition.  In the same way the colour of a lamp indicates what gas is used in street lighting, the instruments of XMM-Newton will reveal the deepest secrets of a source, its chemical composition, temperature, and even the velocity of the source.

European Photon Imaging Cameras (EPIC)

There are three scientific instruments aboard XMM-Newton. The mirror modules will send the image beam along the telescope tube to five cameras at the extremity of the spacecraft. At the prime focus of each of the telescopes, behind six-position filters, are three European Photon Imaging Cameras (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, a grating structure on two mirror modules reflects about half 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/UV Monitor (OM)

The third instrument aboard XMM-Newton is a conventional but very sensitive Optical/UV Monitor (OM), which can observe simultaneously the same regions as the X-ray telescopes, but in the ultraviolet and visible wavelengths. This gives astronomers complementary data about the X-ray sources. In orbit, this 30 cm telescope is as sensitive as a four-metre instrument on the Earth's surface.

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