Swift Gamma-Ray Burst Mission
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| Image:Swift spacecraft.jpg | |
| The Swift Spacecraft (credit: NASA) | |
| Organization | NASA |
| Wavelength regime | gamma-ray/X-ray/UV/optical |
| Orbit Height | 600 km |
| Orbit period | ~90 min |
| Launch date | 20 November 2004 |
| Deorbit date | ? |
| Mass | 1500 kg |
| Webpage | http://swift.gsfc.nasa.gov/ |
| Physical Characteristics | |
|---|---|
| Telescope Style | coded mask (BAT), Wolter I (XRT), reflector (UVOT) |
| Diameter | 30 cm (UVOT) |
| Collecting Area | 5200 cm2 (BAT) |
| Effective Focal Length | 381 cm (UVOT) |
| Instruments | |
| BAT | gamma-ray telescope |
| XRT | X-ray telescope |
| UVOT | UltraViolet/Optical telescope |
The Swift Gamma-Ray Burst Mission consists of an unmanned spacecraft called Swift, which was launched into orbit on November 20, 2004, at 17:16:00 UTC (12:16 PM, EST) on top of a Delta 2 rocket. It is managed by NASA's Goddard Space Flight Center.
Contents |
Overview
Swift is a multi-wavelength space-based observatory dedicated to the study of gamma-ray burst (GRB) science. Its three instruments will work together to observe GRBs and their afterglows in the gamma-ray, X-ray, ultraviolet, and optical wavebands. This mission is part of NASA's "Medium Explorer program" and the satellite was developed by an international consortium from the United States, United Kingdom, and Italy.
During its nominal mission of two years about 200 GRBs should be observed, and as with many other NASA missions, once the two years are concluded successfully the mission will probably be extended. A dedicated telescope will be used to locate the position of each event with an accuracy of 1 to 4 arc-minutes within 15 seconds. The satellite is then able to reorient itself automatically in about 20 to 75 seconds to point all of its instruments at the burst location. This ability is the reason for the mission's name "Swift." In order to achieve this fast slew rate, the observatory is equipped with momentum wheels as part of its reaction control system. These wheels are more massive than any used on past spacecraft, and are therefore more effective at reorienting the spacecraft when they spin.
In the time between GRB events the instruments on board will conduct an all-sky survey in the hard X-ray. After its successful completion, the survey is anticipated to yield new black hole candidates in the sky.
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. The Swift main ground station is located in Malindi on the coast of Eastern Kenya, Africa and is operated by the Italian Space Agency.
Instruments
There are three observing instruments on board:
- Burst Alert Telescope (BAT), 15 - 150 keV energy range. It initially detects a new GRB event and computes its coordinates in the sky.
- X-Ray Telescope (XRT), 0.2 - 10 keV energy range. It can take images and perform spectral analyses of the GRB afterglow. This data will provide a more precise location of the GRB, with an error circle of approximately 6 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.
- UV/Optical Teslescope (UVOT), 170 - 650 nm wavelength range. If an optical afterglow is detected, UVOT provides a sub-arcsecond resolution position for the burst. UVOT also provides photometry through lenticular filters in optical and ultra-violet and spectra through the use of its optical and UV grisms. UVOT is also used to provide long time follow-ups of afterglow lightcurves.
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.
Mission progress
Image:Swift m101 combined low.jpg
- Swift was launched on November 20, 2004, and reached its design orbit of 584x601 km.
- On December 4 the power up of the on-board devices hit a snag, when the Thermo-Electric Cooler (TEC) for the X-ray CCD did not turn on as expected. Mission members are evaluating in what way the science data will be affected, if the TEC is off for the rest of the mission.
- December 17 at 7:28:30 UT, the Swift Burst Alert Telescope (BAT) triggered and located on-board an apparent gamma-ray burst. The spacecraft did not autonomously slew to the burst since automated slewing was not yet enabled.
- Swift had its first GRB trigger during a period when the automatic slew was allowed 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 April 7, 2005, Swift has detected about two dozen GRBs and X-ray afterglows for about 15 of them, and optical afterglows for a few. Optical afterglows are important for providing distance estimates.
Important events and results
On May 9, 2005, Swift detected the flash of two neutron stars crashing together, a burst of gamma rays that lasted one-twentieth of a second. The craft slewed to look towards the direction of the flash and about 53 seconds after the initial burst, the X-ray telescope caught the rapidly fading afterglow of the event. The detection marks the first time that the location of a short-duration gamma-ray burst has been identified. (Cowen, 2005)
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 lightyears.
References
Ron Cowen (2005). Fleeting flash. Pinpointing a short gamma-ray burst. Science News 167 (20): 308.
External links
- NASA's Swift site
- Penn State Swift MOC web site
- Status page on the same site
- Gamma-ray Burst Real-time Sky Map based on Swift data
- Announcement of first Swift GRB
- GCN entry for first GRB observed with auto-slew
- APOD page with movie of separation from rocket
