UVOT (UV/Optical Telescope)

MSSL will build the UV/Optical Telescope (UVOT) for SWIFT. The UVOT will be, as far as possible, an exact copy of the XMM-OM instrument. It is a 30cm diameter modified Ritchey-Chrétien telescope with an f/2.0 primary beam that is re-imaged to f/13 by the secondary. The sky image is recorded on a photon counting, intensified CCD detector, which operates at the ambient temperature of the instrument. The detector covers a field of view of 17-arcmin square with 0.5 arcsec pixels and is sensitive between 170nm and 650nm. A filter wheel provides broadband energy discrimination via filters, together with two grisms for low-resolution spectroscopy and a 4x-image expander for near-diffraction limited imaging. An Instrument Control Unit (ICU) configures the instrument, provides thermal control and interfaces with the spacecraft, while a Data Processing Unit (DPU) intelligently handles the science data.

XMM-OM baffles

A view into the XMM-OM telescope tube showing the arrangement of the baffle vanes.

The UVOT is well suited to the task of studying g -ray bursts. Observing from space, it will benefit from very low sky brightness, excellent spatial resolution and a zero read-noise detector, making its limiting sensitivity comparable with a 4m ground based telescope (a B=24 magnitude star can be detected in 1000s using a white-light filter). Additionally it provides access to the UV region that is inaccessible from the ground.

For 1<z<5, the redshifted Lyman edge falls within the UVOT bandpass, producing a sharp cut-off in flux shortward of the edge. This edge can be detected by 6-band photometry with the UVOT yielding z to an accuracy of roughly 0.1 for a 20 th magnitude star (1000s exposures per filter assumed). For bright bursts (e.g. GRB990123) the redshift can be determined even more accurately by using a Grism to generate a dispersed spectrum. The UVOT will also measure the position of the UV/optical afterglow to an accuracy of 0.3 arcsec or better with respect to field stars, allowing the position of the burst within the host galaxy to be determined. UVOT will provide an optical finding chart of each burst field within 300 seconds of the initial trigger.

Below is a selection of images of the XMM-OM at various stages during the manufacture and test programmes.

Telescope in cleanroom at MSSL.

Flight Model Blue Module.

Filter Wheel mechanisms.

Telescope during vibration testing at CSL.

Preparation for thermal vacuum testing of the telescope.

Assembly of the XMM spacecraft at Dornier.

All images: © UCL, Mullard Space Science Laboratory.

Further Information:

Click here for a link to NASA's SWIFT homepage.

Click here for a link to the XMM-Optical Monitor homepage.

Click here to return to the MSSL homepage.

This page was last updated by Martin de la Nougerede 16th December 1999

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