XMM-Newton 'spare-time' provides impressive sky survey
For the past four years, while ESA’s XMM-Newton X-ray observatory has been
slewing between different targets ready for the next observation, it has kept
its cameras open and used this spare time to quietly look at the heavens. The
result is a 'free-of-charge' mission spin-off – a survey that has now covered an
impressive 25 percent of the sky.
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