Scientists from the University of Leicester analysing data from NASA's Swift satellite have come across a cosmic explosion -- the like of which they have never witnessed before.
The satellite detected a new kind of cosmic event which appears to be a precursor to a supernova, which is expected to reach peak brightness in about a week's time.
Satellites and the world's largest telescopes are now trained on the sight, watching and waiting. The explosion has the trappings of a gamma-ray burst, the most distant and powerful type of explosion known. Yet this explosion, detected on February 18, was about 25 times closer and 100 times longer than the typical gamma-ray burst. And it possesses characteristics never seen before.
Dr Julian Osborne, of the Department of Physics and Astronomy at the University of Leicester, said:
"We are part of the team collecting and understanding the data from the Swift spacecraft on this unique gamma-ray burst. Swift has observed well over a hundred GRBs, but has never seen one like this."
"This is totally new and unexpected," said Neil Gehrels, Swift principal investigator at NASA's Goddard Space Flight Center in Greenbelt, Md. "This is the type of unscripted event in our nearby universe that we hoped Swift could catch."
The explosion, called GRB 060218 after the date it was discovered, originated in a star-forming galaxy about 440 million light-years away toward the constellation Aries. This is the second-closest gamma-ray burst ever detected, if indeed it is a true burst.
The burst of gamma rays lasted for nearly 2,000 seconds; most bursts last a few milliseconds to tens of seconds. The explosion was suprisingly dim however, given its relative closeness, suggesting that scientists might be viewing the event slightly off-axis. Yet this is just one explanation on the table. The standard theory for gamma-ray bursts is that the high-energy light is beamed in our direction.
Dr Osborne added:
"Nearby GRBs are rare, this is probably the closest seen by Swift. It appears much less energetic than normal bursts, but its closeness will allow the associated supernova to be followed in detail. Swift continues to observe GRB 060218 although its X-ray brightness is now only about 0.001% of what it was during the first observation."
Because the burst was so long, Swift was able to observe the bulk of the explosion with all three of its instruments: the Burst Alert Telescope, which detected the burst; and the X-ray Telescope and Ultraviolet/Optical Telescope, which provide high-resolution imagery and spectra across a broad range of wavelengths.
Scientists are making observations with the Hubble Space Telescope, and the Chandra X-ray and XMM-Newton Observatories. The Leicester team is also involved in the ground-based observations being made with the Very Large Telescope in Chile, and with the UK large robotic telescopes will attempt observations with the Hubble Space Telescope and Chandra X-ray Observatory.
Amateur astronomers in dark skies might be able to see the explosion with a 16-inch telescope as it hits 16th magnitude brightness.
The NASA Goddard Space Flight Center manages the Swift project, the satellite is controlled from Penn State University, using a ground station in Kenya.
Swift is a NASA mission with the participation of the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom.
For a before-after image of the explosion and its coordinates, visit:
Gamma-Ray Bursts were only discovered in 1969, and their distance has only been known for eight years. Swift, a mission with substantial UK and Italian participation, is designed to solve the mystery of the origin of gamma-ray bursts. Scientists believe the bursts are related to the formation of black holes throughout the universe - the birth cries of black holes.
To track these mysterious bursts, Swift carries a suite of three instruments. The Burst Alert Telescope (BAT) instrument, built by NASA's Goddard Space Flight Center, detects and locates 2-3 gamma-ray bursts weekly, relaying a rough position to the ground within 20 seconds. The satellite automatically and swiftly re-points itself to bring the burst area into the narrower fields of view of the on-board X-ray Telescope (XRT) and the UltraViolet/Optical Telescope (UVOT). These telescopes study the afterglow of the burst produced by the cooling material that remain from the original explosion.
The XRT (with its Leicester-provided X-ray camera) uniquely finds a precise arc-second position of the burst. The XRT and the UVOT (with the MSSL-provided telescope) measures the spectrum of its afterglow in X-ray and visible wavelengths. For most of the bursts detected, Swift data, combined with complementary observations conducted with ground-based telescopes, enables the distances to the burst sources to be measured.
The afterglow phenomenon can linger in X-ray light, optical light, and radio waves for hours to weeks, providing detailed information about the burst. Swift routinely checks every discoverd burst regularly to study the fading afterglow, often working in conjunction with ground-based optical and radio telescopes.
Swift notifies the astronomical community via the Goddard-maintained Gamma-ray Burst Coordinates Network whenever a new burst is discovered, providing the crucial link of the burst's precise location directly other telescopes. The Swift Mission Operations Center, operated from the Pennsylvania State University campus, controls the Swift observatory and provides continuous burst information. Goddard manages Swift.
Swift is a NASA mission with the participation of the Italian Space Agency (ASI) and the Particle Physics and Astronomy Research Council in the United Kingdom.
Swift was built through collaboration with national laboratories, universities and international partners, including General Dynamics, Gilbert, Arizona; Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; ASI-Malindi ground station in Africa; the ASI Science Data Center in Italy; and the Brera Observatory in Milan, Italy.
The total cost of the mission is £138 million (250 million dollars). The UK contribution, funded by the Particle Physics and Astronomy Research Council, is £3.81 million (plus a further £2.35 million for post launch support).
The UK Swift Science Data Centre is at http://www.swift.ac.uk/
Stars much more massive than the Sun end their lives in an explosion called a supernova. these rare events are normally detected several days or even weeks after the initial explosion as the object gets brighter. In this case the gamma-ray burst jet forced its way out of the dying star and emitted a vast amount of radiation in our direction. This beam of light was detected by Swift and told us where the supernova had occured. Thus the evolution of this supernova can be studied from a much earlier time than for a typical example.
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