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.
for a link to NASA's SWIFT homepage.
for a link to the XMM-Optical Monitor homepage.
to return to the MSSL homepage.
This page was last updated by Martin
de la Nougerede 16th December 1999
to previous page