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.
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.
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 9th
July 1999
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