page_title: Gamma-ray burst
section_title: History
hierarchical_section_title: Gamma-ray burst / History
caption_attribution_description: BATSE All-Sky Plot of Gamma-Ray Burst Locations. Original caption: The above figure illustrates the locations of 2512 gamma-ray bursts detected by the BATSE instrument after more than eight years of observation. Statistical tests confirm that the bursts are isotropically distributed on the sky - no significant quadrupole moment or dipole moment is found. At the same time, a deficiency has been detected in the number of faint bursts, interpreted as an indication that the spatial extent of the burst distribution is limited and that BATSE sees the limit or edge of the distribution. The nature of the sources remains unknown. However, their isotropic distribution on the sky along with the deficiency of faint bursts can be naturally explained if the bursts are located at cosmological distances (far beyond the Milky Way). This interpretation has been confirmed in recent years via distance estimates for optical counterparts to gamma-ray bursts.
context_page_description: Gamma-ray bursts are flashes of gamma rays from extremely energetic explosions. They have been seen in distant galaxies. They are the most luminous electromagnetic events known to occur in the universe.
  Bursts can last from milliseconds to several minutes, although a typical burst lasts a few seconds. The initial burst is usually followed by a longer-lived 'afterglow' emitted at longer wavelengths.
  Most GRBs are a narrow beam of intense radiation released during a supernova, as a huge rapidly spinning star collapses to form a black hole. A subclass of GRBs seem to come from a different process, perhaps the merger of binary neutron stars.
  The sources of most GRBs are billions of light years away from Earth. This suggests the explosions are extremely energetic: a typical burst releases as much energy in a few seconds as the Sun will in its entire 10 billion year lifetime. They are very rare.
  All observed GRBs have come from outside the Milky Way galaxy. Similar phenomena, soft gamma repeater flares, are associated with magnetars within the Milky Way. It has been suggested that a gamma-ray burst in the Milky Way could cause a mass extinction on Earth. No such case is known.
context_section_description: Gamma-ray bursts were first observed in the late 1960s by the U.S. Vela satellites, which were built to detect gamma radiation pulses emitted by nuclear weapons tested in space.
  On July 2, 1967, at 14:19 UTC, the Vela 4 and Vela 3 satellites detected a flash of gamma radiation unlike any known nuclear weapons signature. Uncertain what had happened but not considering the matter particularly urgent, the team at the Los Alamos Scientific Laboratory filed the data away for investigation.
  By analyzing the different arrival times of the bursts as detected by different satellites, the team was able to determine rough estimates for the sky positions of sixteen bursts¹²⁻¹⁶ and definitively rule out a terrestrial or solar origin.  The discovery was published in 1973.
caption: Positions on the sky of all gamma-ray bursts detected during the BATSE mission.  The distribution is random, with no concentration towards the plane of the Milky Way, which runs horizontally through the center of the image.
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