The XMM-Newton Optical Monitor

 

The Optical/UV Monitor Telescope (XMM-OM) is mounted on the mirror support platform of XMM-Newton alongside the X-ray mirror modules. It provides coverage between 170 nm and 650 nm of the central 17 arc minute square region of the X-ray field of view, permitting routine multiwavelength observations of XMM targets simultaneously in the X-ray and ultraviolet/optical bands.

The XMM-OM consists of a Telescope Module and a separate Digital Electronics Module, of which there are two identical units for redundancy. The Telescope Module contains the telescope optics and detectors, the detector processing electronics and power supply. There are two distinct detector chains, again for redundancy. The Digital Electronics Module houses the Instrument Control Unit, which handles communications with the spacecraft and commanding of the instrument, and the Data Processing Unit, which pre-processes the data from the instrument before it is telemetered to the ground.

The Telescope Module consists of a modified 30 cm Ritchey-Chretien telescope with a focal ratio of f/12.7, i.e. a focal length of ca. 3.8 m. The incoming light is reflected by a mirror inclined at an angle of 45° to one of two redundant detectors. The OM telescope tube is ca. 2 m long. Incoming light falls onto the primary mirror, which reflects it onto the secondary, from where it goes to the inclined mirror that reflects it onto the detector. A filter wheel is mounted immediately in front of the detectors . This does not only contain filters, but also other optical elements, like grisms and a magnifier (i.e. optics for a longer focal length and thus higher resolution on the sky).

 

OM Main Characteristics

  • 2 m long telescope tube.
  • 30 cm Ritchey-Chretien telescope.
  • Focal ratio of f/12.7 and focal length of 3.8 m
  • Total coverage between 170 nm and 650 nm of a 17 arcmin square field of view.
  • A primary mirror of 0.3 m and a hyperboloid secondary mirror.
  • Two (redundant) filter wheels with 11 apertures: one blanked off, six broad band filters (U, B, V, UVW1, UVM2 and UVW2), one white, one magnifier and two grisms (UV and optical).
  • Two (redundant) detectors: micro-channel plate intensified CCD with 384 x 288 physical pixels (Active area 256x256). Photon events centroided to 1/8 physical pixel.
  • Two (redundant) Digital Electronics Module.

 

 

A schematic of the Optical Monitor

XMM OM Diagram

Click below for more details on the components of Optical Monitor.

[baffle]  [detector]  [filter]  [processing electronics]  [telescope power supply]  [digital electronics module]

 

The XMM Optical Monitor was built by a consortium of institutes from the UK, the USA and Belgium, led by the PI group at the Department of Space and Climate Physics at the Mullard Space Science Laboratory, part of University College London.

 

References

K.O. Mason et al. 2001, A&A 365, L36
Mullard Space Science Laboratory: The XMM Optical Monitor Home Page


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