The UV/optical telescope (UVOT) is one of three instruments flying aboard the Swift Gamma-ray Observatory. It is designed to capture the early (~1 minute) UV and optical photons from the afterglow of gamma-ray bursts as well as long term observations of these afterglows. This is accomplished through the use of UV and optical broadband filters and grisms. The UVOT has a modified Ritchey-Chretien design with micro-channel plate intensified charged-coupled device detectors that provide sub-arcsecond imaging. Unlike most UV/optical telescopes the UVOT can operate in a photon-counting mode as well as an imaging mode. We discuss some of the science to be pursued by the UVOT and the overall design of the instrument.
The SWIFT/UVOT has a requirement for on-board autonomous control of exposures, health and safety. It is anticipated that the optimal form of control may not emerge until after launch and may change during the course of the mission. A flexible and readily re-configurable system is therefore required. Two schemes have been adopted. As well as the more usual approach of tables of experimental configurations, action tables mapping command sequences to key events have been implemented. The command sequences, consisting of a series of command words located in EEPROM, are executed using a stack-based software 'virtual CPU.' Each command word, analogous to hardware CPU assembler instructions, results in the execution of well-checked Ada code fragments. As well as implementing the UVOT commands, the code includes functionality such as delaying a specified time, awaiting action completion, 'subroutine' calls and simple flow control. These permit the construction of complex control sequences. A C-like language is used to describe the required sequences. A translator converts them to the required command word sequence that is then validated on a simulator. Reloading the command sequence or the tables referring to it alters the autonomous behavior of the instrument.
The Swift MIDEX mission is the first-of-its-kind observatory for multi-wavelength transient astronomy. The goal of the mission is to ascertain the origin of gamma-ray bursts and to utilize these bursts to probe the early universe. The Ultra- Violet/Optical Telescope (UVOT) is one of three telescopes flying aboard Swift. The UVOT is a working 'copy' of the Optical Monitor on the X-ray Multi-mirror Mission (XMM- Newton). It is a Ritchey-Chretien telescope with microchannel plate intensified charged-coupled devices (MICs) that provide sub-arcsecond imaging. These MICs are photon counting devices, capable of detecting very low signal levels. When flown above the atmosphere, the UVOT will have the equivalent sensitivity of a 4 m telescope on the ground, reaching a limiting magnitude of 24 for a 1000 second observation in the white light filter. A rotating filter wheel contains sensitive photometric broadband UV and visual filters for determining photometric redshifts. The filter wheel also contains UV and visual grisms for performing low-resolution spectroscopy.
A multi-national consortium of research groups are developing the XMM (x-ray multi-mirror mission) optical monitor to provide a capability for optical identification and photometry of x-ray sources observed by the XMM observatory. This will be the first multi-wavelength facility dedicated to monitoring the variability of diverse sources from the optical through to x-ray wavelengths. Here we describe the system design and discuss progress in the breadboard phase of the development program.
The main design features and the early findings of the Rosat XUV wide field camera (WFC) are discussed. The most important data on the WFC telescope and detectors are presented. The WFC operational features, observing efficiency, filter performance, thermal performance star tracker performance, and single-event upsets are discussed. The first WFC images are compared with preflight calibration data.