On the tenth anniversary of its launch, NASA's Swift Gamma-ray Burst Explorer -- an orbiting space observatory with major and continuing contributions from Pennsylvania State University (Penn State) scientists -- is recognised as one of the most versatile astrophysics missions ever flown.
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|In the most common type of gamma-ray burst, illustrated here, a dying massive star forms a black hole (left), which drives a particle jet into space. Light across the spectrum arises from hot gas near the black hole, collisions within the jet, and through the jet's interaction with its surroundings. Image Credit: NASA's Goddard Space Flight Center || |
It remains the only satellite that can precisely locate gamma-ray bursts -- the universe's most powerful explosions. It also is the only satellite that can monitor the explosions in space across a broad range of wavelengths using multiple instruments before these powerful bursts fade from view.
Swift carries two telescopes whose lead scientists are Penn State astronomers and a third telescope led by a NASA scientist.
Science and flight operations for Swift are controlled by Penn State from the Mission Operations Center at the University Park campus. Earlier this year, NASA gave its top ranking to the Swift observatory for astronomy satellites other than two of its ''great observatories,'' the Hubble Space Telescope and Chandra X-ray Observatory.
''Swift'' is a core capability designed into the spacecraft to empower it to swiftly detect gamma-ray bursts (GRBs), which typically last less than a minute. When Swift observes a GRB, it automatically determines the blast's location, broadcasts the position to the astronomical community, and then turns toward the site to investigate with its own sensitive telescopes.
''This process can take as little as 40 seconds, which is so quick we sometimes catch the tail end of the GRB itself,'' says John Nousek, Swift's director of mission operations and a professor of astronomy and astrophysics at Penn State University. ''Because Swift autonomously responds to sudden bursts of high-energy light, it also provides us with data on a wide range of short-lived events, such as X-ray flares from stars and other objects.''
Swift carries three telescopes, two of which are led by Penn State astronomers. The lead scientist for Swift's X-ray Telescope is David Burrows, a professor of astronomy and astrophysics. The lead scientist for Swift's Ultraviolet/Optical Telescope is Michael Siegel, a senior research scientist.
To date, Swift has detected more than 900 GRBs. Swift detects one event about twice a week. Its discoveries include a new ultra-long class of gamma-ray bursts, whose high-energy emissions endure for hours.
Swift's discoveries also include the farthest GRB, whose light took more than 13 billion years to reach us; and the "naked-eye" GRB, which for about a minute was bright enough to see with the naked eye despite the fact that its light had traveled 7.5 billion years.
Early in the mission, Swift observations provided the "smoking gun" that validated long-standing theoretical models suggesting that GRBs with durations under two seconds come from mergers of two neutron stars, objects with the mass of the Sun that have been crushed to the size of a city.
In addition to its studies of GRBs, Swift conducts a wide array of observations of other astrophysical phenomena. A flexible planning system enables astronomers to request Swift "target-of-opportunity" (TOO) observations, which can be commanded from the ground in as little as 10 minutes, or to set up monitoring programs for observing specific sources for a few minutes to multiple months. The system can schedule up to 75 independent targets a day.
"These characteristics make Swift a pioneer in a burgeoning field we call 'time-domain' astronomy," said Neil Gehrels, the mission's principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Maryland. "Just as we extended telescopic astronomy from visible light to other wavelengths, we now are beginning to study how the properties of astronomical objects change across a wide range of timescales, from less than a second to decades."
Some projects require years of observations, such as long-term monitoring of the centre of our galaxy with Swift's X-Ray Telescope (XRT) -- including its dormant super-massive black hole. Astronomers also are using the spacecraft's Burst Alert Telescope to conduct a continuing survey of more than 700 active galaxies, where monster black holes devour large amounts of gas and shine brightly in X-rays and gamma rays.
Shorter-term projects have included observations to map the nearest galaxies in ultraviolet (UV) wavelengths. The most demanding of these objects was the Large Magellanic Cloud, a small satellite galaxy orbiting our own at a distance of about 163,000 light-years. Swift's Ultraviolet/Optical Telescope (UVOT) captured 2,200 overlapping "snapshots" to cover this galaxy, producing the best-ever view of its ultraviolet emissions. "The UVOT is the only telescope that can produce high-resolution wide-field multicolor surveys in the ultraviolet," said Michael Siegel, who leads the UVOT instrument team at Penn State.
In 10 years of operation, Swift has made 315,000 individual observations of 26,000 separate targets, supporting nearly 6,200 target-of-opportunity requests by more than 1,500 scientists. Swift's observations range from optical and ultraviolet studies of comets and asteroids to catching X-rays and gamma-rays from some of the most distant objects in the universe.
Another major highlight of Swift's studies of some 300 supernovae was the 2008 discovery of X-ray signals produced by a star caught in the act of exploding. Shockwaves breaching the surface of the dying star produced this brilliant X-ray flash.
Swift rocketed into orbit on November 20, 2004. Managed by NASA Goddard, the mission is operated in collaboration with Penn State, the Los Alamos National Laboratory in New Mexico, and Orbital Sciences Corporation in Dulles, Virginia. Other partners include the University of Leicester and Mullard Space Science Laboratory in the United Kingdom, Brera Observatory and the Italian Space Agency in Italy, with additional collaborators in Germany and Japan.
Swift will continue its enormously productive scientific work through at least 2016.