gamma-ray bursts

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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 ?
Kodama, "Redshift dependent lag-luminosity relation in 565 baste gamma ray bursts," in Proceedings of the Santa Fe Conference on Gamma-Ray Bursts 2007, GRB 2007, pp.
Briggs said their observations show that gamma ray bursts are less common in the immediate universe.
Scientists might be able to detect warning signs of an impending gamma ray burst. But if a burst were headed for Earth -- and the chances of that happening are close to zero, astronomers say -- there wouldn't be anything anybody could do about it.
Nial Tanvir of the University of Leicester, who led the research, said: "This observation finally solves the mystery of the origin of short gamma ray bursts.
THE mystery of the forces behind the most powerful explosions in the Universe - Gamma Ray Bursts - has been solved by Liverpool scientists.
Carole Mundell, Head of the ARI Gamma Ray Burst team, said: "Gamma Ray Bursts are the most powerful explosions in the universe and their origin remains one of the key outstanding issues in modern astronomy.
By some calculations, the gamma ray burst release equalled as much energy in one second as all of the tenbillion trillion stars in the universe combined.
The cataclysmic blast, known as a gamma ray burst, had taken nine billion years to reach earth.
"You can think of a cosmic gamma ray burst as someone switching on a light, leaving it on for a bit, and turning it off.
Dr Sarri, from Queen's School of Mathematics and Physics, has led an international team of researchers to create the first small-scale replica of e n gamma ray bursts. He says he has now been able to prove for the first time, some of the "key phenomena that play a major role in producing gamma ray bursts".
Analyzing their properties, scientists noticed something unusual in the way lightning occurs and causes gamma ray bursts. These gamma ray bursts coincided with that part of the spectrum which is usually associated with the process of antimatter annihilation, something physicists have never seen before. 
This volume collects 11 talks from a meeting convened to celebrate the life of the late Polish astronomer Bohdan Paczynski (1940-2007), whose main work involved the theory of the evolution of stars, accretion discs, and gamma ray bursts. Memorial and biographical talks are followed by presentations on black hole accretion disks, the All Sky Automated Survey, cosmic dark matter and gravitational microlensing, the Optical Gravitational Lensing Experiment, Paczynski's contributions to understanding gamma ray bursts, and the place of Paczynski in the history of astronomy.