Swift Gamma-Ray Burst Mission
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| Swift Gamma-Ray Burst Mission ("Swift") | |
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(credit: NASA)
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| General information | |
| Organization | NASA |
| Launch date | 20 November 2004 |
| Mission length | 6 years[1] (may be further extended) |
| Deorbited | no sooner than 2020 |
| Mass | 1500 kg |
| Orbit height | 600 km |
| Orbit period | ~90 min |
| Telescope style | coded mask (BAT) Wolter I (XRT) Ritchey-Chrétien (UVOT) |
| Wavelength | γ-ray / X-ray / UV / optical |
| Diameter | 30 cm (UVOT) |
| Collecting area | 5200 cm2 (BAT) |
| Focal length | 381 cm (UVOT) |
| Instruments | |
| BAT | Burst Alert (gamma-ray) Telescope |
| XRT | X-Ray Telescope |
| UVOT | UltraViolet/Optical telescope |
| Website http://swift.gsfc.nasa.gov/ |
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The Swift Gamma-Ray Burst Mission consists of a robotic spacecraft called Swift, which was launched into orbit on November 20, 2004, at 17:16:00 UTC (12:16 PM, EST) by a Delta II 7320-10C expendable launch vehicle. Swift is managed by the NASA Goddard Space Flight Center, was developed by an international consortium from the United States, United Kingdom, and Italy and is part of NASA's "Medium Explorer Program" (MIDEX).
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[edit] Overview
Swift is a multi-wavelength space-based observatory dedicated to the study of gamma-ray burst (GRB) science. Its three instruments work together to observe GRBs and their afterglows in the gamma-ray, X-ray, ultraviolet, and optical wavebands.
Based on continuous scans of the area of the sky which one of the instruments monitors, Swift uses momentum wheels to autonomously slew into the direction of possible GRBs. The mission name "Swift", which is not an acronym, refers to this rapid slew capability and the nimble bird of the same name.[2] All discoveries of Swift are quickly sent to the ground and that data is available to other observatories which join Swift in observing the GRBs.
In the time between GRB events, Swift is available for other science and scientists can submit proposals for observations.
The Swift Mission Operation Center (MOC), where commanding of the satellite is performed, is located in State College, Pennsylvania and operated by the Pennsylvania State University and industry subcontractors. The Swift main ground station is located in Malindi on the coast of Eastern Kenya, Africa and is operated by the Italian Space Agency. The Swift Science Data Center (SDC) and archive are located at the Goddard Space Flight Center. The UK Swift Science Data Centre is located at the University of Leicester.
The Swift spacecraft bus was built by Spectrum Astro (now a part of General Dynamics Advanced Information Systems).[3]
[edit] Instruments
[edit] Burst Alert Telescope (BAT)
The BAT detects GRBs events and computes its coordinates in the sky. It covers a large fraction of the sky (over one steradian fully coded, three steradians partially coded -- by comparison, the full sky solid angle is 4π or about 12.6 steradians). It locates the position of each event with an accuracy of 1 to 4 arc-minutes within 15 seconds. This crude position is immediately relayed to the ground and some wide-field, rapid-slew ground telescopes can catch the GRB with this information. BAT uses a coded-aperture mask of 5 mm lead tiles, above a detector plane of 4 mm CdZnTe tiles; it is purpose-built for Swift. Energy range: 15 - 150 keV
[edit] X-ray Telescope (XRT)
The XRT can take images and perform spectral analyses of the GRB afterglow. This provides more precise location of the GRB, with an error circle of approximately 3.5 arcseconds radius. The XRT is also used to perform long term monitoring of GRB afterglow light-curves for days to weeks, depending on the brightness of the afterglow. The XRT is primarily composed of the X-ray mirrors from the JET-X mission, with the detector upgraded to a single MOS CCD similar to those used by the XMM-Newton EPIC MOS cameras. Energy range: 0.2 - 10 keV.
[edit] Ultraviolet/Optical Telescope (UVOT)
After Swift has slewed towards an GRB, the UVOT is used to detect an optical afterglow. UVOT provides a sub-arcsecond resolution position and provides photometry through lenticular filters in optical and ultra-violet and spectra (170–650 nm) through the use of its optical and UV grisms. UVOT is also used to provide long time follow-ups of afterglow lightcurves. UVOT is based on the XMM-Newton mission's Optical Monitor (OM) instrument, with upgraded onboard processing computers.
[edit] Science goals
This mission has multiple science goals:
- Determine the origin of GRBs. There seem to be at least two types of GRBs, only one of which can be explained with a hypernova, creating a gamma-ray beam. More data is needed to explore other explanations.
- GRBs seem to take place at "cosmological distances," which means they can be used to probe the distant, and therefore young, universe.
- The all-sky survey will be more sensitive than any previous one, and will add significantly to our knowledge of astronomical X-ray sources. Thus, it could also yield unexpected results.
- Swift is also utilized as a general purpose gamma-ray/X-ray/optical observatory platform, performing rapid "Target of Opportunity" observations of many transient astrophysical phenomena, such as supernovae.
[edit] Mission progress
- Swift was launched on November 20, 2004, and reached a near-perfect orbit of 586x601 km altitude with an inclination of 20°.
- On December 4 an anomaly occurred during instrument activation when the Thermo-Electric Cooler (TEC) Power Supply for the X-Ray Telescope did not turn on as expected. The XRT Team at Leicester and Penn State University was able to determine on December 8 that the XRT would be usable even without the TEC being operational. Additional testing on December 16 did not yield any further information as to the cause of the anomaly.
- December 17 at 7:28:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board an apparent gamma-ray burst during launch and early operations. The spacecraft did not autonomously slew to the burst since normal operation had not yet begun, and autonomous slewing was not yet enabled.
- Swift had its first GRB trigger during a period when the autonomous slewing was enabled on January 17, 2005, at about 12:55 UT. It pointed the XRT telescope to the on-board computed coordinates and observed a bright source in the field of view.
- On February 1, 2005 the mission team released the "first light" picture of the UVOT instrument and declared Swift operational.
- As of December 1, 2005, Swift has detected more than 90 GRBs and X-ray afterglows for about 70 of them, and optical afterglows for about 20 of them (40 including ground-based optical observations).
[edit] Important events and results
- On May 9, 2005, Swift detected GRB 050509b, a burst of gamma rays that lasted one-twentieth of a second. The detection marks the first time that the location of a short-duration gamma-ray burst has been identified.
- On September 4, 2005, Swift detected GRB 050904 with a redshift value of 6.29 and a duration of 200 seconds (most of the detected bursts last about 10 seconds). It was also found to be the most distant at approximately 12.6 billion light years.
- On February 18, 2006, Swift detected GRB 060218, an unusually long (about 2000 seconds) and nearby (about 440 million light years) burst which was unusually dim despite its close distance, and may be an indication of an imminent supernova.
- On June 14, 2006, Swift detected GRB 060614, a burst of gamma rays that lasted 102 seconds in a distant galaxy (about 1,6 Billion light years). This GRB is recognized as a type of cosmic explosion called a hybrid gamma-ray burst. As with other gamma-ray bursts, this hybrid blast is likely signaling the birth of a new black hole.
- On March 19, 2008, Swift detected GRB 080319B, a burst of gamma rays amongst the brightest celestial objects ever witnessed. At a distance of 7.5 Billion light years, it established a new record for farthest object (briefly) visible to the naked eye. It is also said to be 2.5 million times intrinsically brighter than the previous brightest accepted supernova.
- On that same day, Swift observed a record four GRBs, hence the "B" suffix indicating the record burst was the second. Incidentally, as noted by NASA's press release, this happened quickly after the death of noted science-fiction writer Arthur C. Clarke.
- On January 9, 2008, Swift was observing a supernova in NGC 2770 when it witnessed an X-ray burst coming from the same galaxy. The source of this burst was found to be the beginning of another supernova, later called SN 2008D. Never before had a supernova been seen at such an early stage in its evolution. Following this stroke of luck (position, time, most appropriate instruments), astronomers were able to study in detail this Type Ibc supernova with the Hubble Space Telescope, the Chandra X-ray Observatory, the Very Large Array in New Mexico, the Gemini North telescope in Hawaii, the Keck I telescope in Hawaii, the 200-inch and 60-inch telescopes at the Palomar Observatory in California, and the 3.5-meter telescope at the Apache Point Observatory in New Mexico. The significance of this supernova was likened by discovery team leader Dr. Alicia Soderberg to that of the Rosetta Stone for egyptology.
[edit] References
- ^ NASA Swift Mission Extended for 4 More Years. Omitron. Retrieved on 2008-04-07.
- ^ Swift: Frequently Asked Questions
- ^ Swift. GD.
[edit] External links
- NASA Swift site at GSFC
- Swift Mission Director's Status Report Log
- Sonoma State University Swift website
- Penn State Swift Mission Operations Center site
- Gamma-ray Burst Real-time Sky Map based on Swift data
- Swift Short-Burst Discovery
- Announcement of first Swift GRB
- GCN entry for first GRB observed with auto-slew
- APOD page with movie of separation from rocket
- New Scientist: Swift measures distance to gamma-ray bursts
- Press release concerning the March 19 record GRBs
- Press release concerning the January 2008 supernova
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