[Show abstract][Hide abstract] ABSTRACT: The Ultraviolet/Optical Telescope (UVOT) is one of three instruments onboard the Swift observatory. The photometric calibration has been published, and this paper follows up with details on other aspects of the calibration including a measurement of the point spread function with an assessment of the orbital variation and the effect on photometry. A correction for large-scale variations in sensitivity over the field of view is described, as well as a model of the coincidence loss which is used to assess the coincidence correction in extended regions. We have provided a correction for the detector distortion and measured the resulting internal astrometric accuracy of the UVOT, also giving the absolute accuracy with respect to the International Celestial Reference System. We have compiled statistics on the background count rates, and discuss the sources of the background, including instrumental scattered light. In each case, we describe any impact on UVOT measurements, whether any correction is applied in the standard pipeline data processing or whether further steps are recommended.
Monthly Notices of the Royal Astronomical Society 06/2010; 406(3):1687 - 1700. DOI:10.1111/j.1365-2966.2010.16832.x · 5.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: We present the photometric calibration of the Swift UltraViolet/Optical Telescope (UVOT) which includes: optimum photometric and background apertures, effective area curves, colour transformations, conversion factors for count rates to flux, and the photometric zero points (which are accurate to better than 4 per cent) for each of the seven UVOT broadband filters. The calibration was performed with observations of standard stars and standard star fields that represent a wide range of spectral star types. The calibration results include the position dependent uniformity, and instrument response over the 1600-8000A operational range. Because the UVOT is a photon counting instrument, we also discuss the effect of coincidence loss on the calibration results. We provide practical guidelines for using the calibration in UVOT data analysis. The results presented here supersede previous calibration results. Comment: Minor improvements after referees report. Accepted for publication in MNRAS
[Show abstract][Hide abstract] ABSTRACT: The UV/Optical Telescope (UVOT) is one of three instruments flying aboard the
Swift Gamma-ray Observatory. It is designed to capture the early (approximately
1 minute) UV and optical photons from the afterglow of gamma-ray bursts in the
170-600 nm band 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 record the arrival time of
individual photons and provide sub-arcsecond positioning of sources. We discuss
some of the science to be pursued by the UVOT and the overall design of the
Space Science Reviews 07/2005; 120(3). DOI:10.1007/s11214-005-5095-4 · 6.28 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Proceedings of SPIE - The International Society for Optical Engineering 01/2003; DOI:10.1117/12.505657 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Proceedings of SPIE - The International Society for Optical Engineering 12/2000; DOI:10.1117/12.409161 · 0.20 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The XMM-OM instrument extends the spectral coverage of the XMM-Newton observatory into the ultraviolet and optical range. It provides imaging and time-resolved data on targets simultaneously with observations in the EPIC and RGS. It also has the ability to track stars in its field of view, thus providing an improved post-facto aspect solution for the spacecraft. An overview of the XMM-OM and its operation is given, together with current information on the performance of the instrument. Comment: Accepted by A&A for publication in the Special Issue on 1st science with XMM Newton, 9 pages
Astronomy and Astrophysics 11/2000; 365(1). DOI:10.1051/0004-6361:20000044 · 4.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: 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.
Society of Photo-Optical Instrumentation Engineers (SPIE) Conference Series; 06/1994