3.2 X-ray Telescopes
XMM-Newton's three X-ray telescopes are co-aligned with a relative astrometry
between the three EPIC cameras calibrated to better than 1-2" across the
full FOV. One telescope has a light path as shown in
Fig. 2; the two others have grating assemblies in their
light paths, diffracting part of the incoming radiation onto their
The light path in XMM-Newton's open X-ray telescope
with the pn camera in focus (not to scale).
Fig. 3 shows the light path in the latter two X-ray
telescopes on board XMM-Newton. Ca. 44% of the incoming light focused by the
multi-shell grazing incidence mirrors is directed onto the camera at
the prime focus, while 40% of the radiation is dispersed by a grating
array onto a linear strip of CCDs. The remaining light is absorbed by
the support structures of the RGAs.
The light path in the two XMM-Newton telescopes with
grating assemblies (not to scale). Note that the actual fraction of
the non-intercepted light that passes to the primary MOS focus
is 44%, while 40% of the incident light is intercepted by grating
plates of the RGA.
The focal instruments are described in §§ 3.3, 3.4 and 3.5. First we explain the most important properties of the
The performance of each X-ray telescope is characterised by:
- the image quality,
- the effective area, and
- the straylight rejection efficiency,
which will be described in the following sections.
European Space Agency - XMM-Newton Science Operations Centre