gamma-ray bursts

gamma-ray bursts

Intense flashes of hard X-rays or gamma rays, detected at energies up to one million electronvolts. They are of short duration (0.1–1000 seconds) and were discovered by US Air Force satellites in 1967 but not declassified until 1973. There are sharp temporal features in the burst time profile; this allows the measurement of differences in arrival times of wavefronts of the order of a few milliseconds over baselines separated by hundreds of light-seconds. For the strongest and most rapidly varying bursts, such measurements yield angular resolutions of the order of arc seconds. The most intense burst observed so far lies within the supernova remnant N49 in the Large Magellanic Cloud. The BATSE experiment on the Compton Gamma Ray Observatory has detected hundreds of γ-ray bursts, averaging about one per day. Measurements have revealed that the distribution of the bursts is consistent with isotropy: they are uniformly distributed across the sky. Their origin still remains a mystery. γ-ray emission lines in their spectra may be related to annihilation radiation redshifted by the strong gravitational field of a neutron star, and γ-ray absorption features to cyclotron absorption in intense magnetic fields. The rapid temporal structure, including the periodic emission, is generally assumed to point to neutron star origins for γ-ray bursts, although sources at cosmological distances cannot be ruled out. The most probable energy source is thought to be either gravitational or nuclear in origin.

gamma-ray bursts

[′gam·ə ‚rā ‚bərsts]
(astronomy)
Intense blasts of soft gamma rays of unknown origin, which range in duration from a tenth of a second to tens of seconds and occur several times a year from sources widely distributed over the sky.
References in periodicals archive ?
Usually, gamma-ray bursts mark the destruction of a massive star, and flaring emission from these events never lasts more than a few hours.
The new finding "is exciting because gamma-ray bursts are showing them selves as a unique probe of the early universe that really hadn't been considered," Joshua Bloom of the University of California, Berkeley reported on January 4.
The connection between Gamma-Ray Bursts (GRBs) and their afterglows is currently not well understood.
Short gamma-ray bursts as observed with satellites like XMM Newton, Fermi or Swift release within a second the same amount of energy as our galaxy in one year.
For now, Fermi's flurry of initial findings--which include discoveries about gamma-ray bursts as well as a possible new class of pulsars, the rapidly spinning corpses of exploded stars--poses new puzzles.
As with other gamma-ray bursts, this hybrid blast is likely signaling the birth of a new black hole.
Gamma-Ray Bursts (GRB) are the most luminous objects in the universe.
Gamma-ray bursts come in two varieties-long and short-depending on how long the flash of gamma rays lasts.
Among the first findings: The high-energy share of gamma-ray bursts arrives at Earth significantly later than the low-energy portion, Peter Michelson and Aurelien Bouvier of Stanford University report.
Most gamma-ray bursts last no longer than about ten seconds, so speed is essential to detect and study the bursts.
No gamma rays or X-rays were detected in association with the flashes, and the astronomers have ruled out the flashes being from phenomena such as gamma-ray bursts, the merger of two neutron stars, merging black holes, or evaporating black holes.
The Swift satellite was built to record gamma-ray bursts, the most energetic explosions in the universe.