XMM-Newton is a European Space Agency (ESA) X-ray observatory, orbiting the Earth. Launched in December 1999, it is the largest scientific satellite ever built in Europe.
As mentioned in my previous post, X-rays cannot penetrate the Earth’s atmosphere, so any observations of astronomical X-rays must be done by telescopes in orbit.
‘XMM’ stands for ‘X-Ray Multi-Mirror Mission’. The ‘Newton’ part was added in honour of Sir Isaac Newton.
Announcing the new name on 9 February 2000, ESA’s former Director of Science Prof. Roger Bonnet explained: “We have chosen this name because Sir Isaac Newton was the man who invented spectroscopy and XMM is a spectroscopy mission. The name of Newton is associated with the falling apple, which is the symbol of gravity and with XMM I hope that we will find a large number of black hole candidates which are of course associated with the theory of gravity. There was no better choice than XMM-Newton for the name of this mission“.
From the ESA website [10/07/2013]
The orbit of XMM-Newton is very eccentric (very oval) and has the Earth very close to one side. At its furthest distance from the Earth, XMM-Newton reaches almost a third of the way to the Moon. This orbit is important for two reasons: to take the spacecraft outside the radiation belts surrounding the Earth to protect both the instruments and data, and to allow for long observation periods which aren’t disrupted by the Earth’s shadow.
XMM-Newton’s orbit has gradually changed since the start of the mission (original orbit shown above), but still takes almost exactly 48 hours for each orbit. This is to ensure the greatest contact time between the spacecraft and ground centre for communications. Out of the 48 hours in each orbit, roughly 40 are usable for observation time; for the other eight hours XMM-Newton is below and within the radiation belts mentioned above.
XMM-Newton is a ‘Multi-Mirror’ mission because it has three X-ray mirrors. X-ray telescopes have a very different design to optical reflection or refraction telescopes you may have at home. X-rays are mostly absorbed if they directly hit (perpendicular to) a surface, so they must be gently angled towards a focus through a mirrored tube (see image a little further below).
XMM-Newton has three main scientific instruments:
- The European Photon Imaging Camera (EPIC) on all three mirrors,
- The Reflection Grating Spectrometer (RGS) on two of the mirrors,
- The Optical Monitor (OM) running parallel to the X-ray mirrors.
The two telescopes which include the RGS instrument deflect off about 40% of their light to a secondary focus, which is where the RGS detector is. It is this instrument I am most interested in, as it produces the high resolution X-ray spectra I will be analysing. More information about X-ray spectroscopy (the study of spectra) will follow in a later post.
There is much more information about XMM-Newton available from ESA, here.