|
The history of gamma-ray burst research began with the serendipitous detection of a gamma-ray burst (GRB) on July 2, 1967, by the U.S. Vela satellites. After these satellites detected fifteen other GRBs, Ray Klebesadel of the Los Alamos National Laboratory published the first paper on the subject, ''Observations of Gamma-Ray Bursts of Cosmic Origin''.〔() "Observations of Gamma-Ray Bursts of Cosmic Origin" Klebesadel R.W., Strong I.B., and Olson R.A. 1973, Ap.J.(Letters) 182, L85〕 As more and more research was done on these mysterious events, hundreds of models were developed in an attempt to explain their origins. ==Discovery== Gamma-ray bursts were discovered in the late 1960s by the U.S. Vela nuclear test detection satellites. The Velas were built to detect gamma radiation pulses emitted by nuclear weapon tests in space. The United States suspected that the USSR might attempt to conduct secret nuclear tests after signing the Nuclear Test Ban Treaty in 1963. While most satellites orbited at about 500 miles above Earth's surface, the Vela satellites orbited at an altitude of 65,000 miles. At this height, the satellites orbited above the Van Allen radiation belt, which reduced the noise in the sensors. The extra height also meant that the satellites could detect explosions behind the moon, a location where the United States government suspected the Soviet Union would try to conceal nuclear weapon tests. The Vela system generally had four satellites operational at any given time such that a gamma-ray signal could be detected at multiple locations. This made it possible to localize the source of the signal to a relatively compact region of space. While these characteristics were incorporated into the Vela system to improve the detection of nuclear weapons, these same characteristics were what made the satellites capable of detecting gamma-ray bursts.〔Katz 2002, p. 4–5〕 On July 2, 1967, at 14:19 UTC, the Vela 4 and Vela 3 satellites detected a flash of gamma radiation that were unlike any known nuclear weapons signatures.〔Schilling 2002, p.12–16〕 Nuclear bombs produce a very brief, intense burst of gamma rays less than one millionth of a second. The radiation then steadily fades as the unstable nuclei decay. The signal detected by the Vela satellites had neither the intense initial flash nor the gradual fading, but instead there were two distinct peaks in the light curve.〔 Solar flares and new supernovas were the two other possible explanations for the event, but neither had occurred on that day.〔 Unclear on what had happened, but not considering the matter particularly urgent, the team at the Los Alamos Scientific Laboratory, led by Ray Klebesadel, filed the data away for later investigation. Vela 5 was launched on May 23, 1969. Because the sensitivity and time resolution on these satellites were significantly more accurate than the instruments on Vela 4, the Los Alamos team expected these new satellites to detect more gamma-ray bursts. Despite an enormous amount of background signals picked up by the new detectors, the research team found twelve events which had not coincided with any solar flares or supernovas. Some of the new detections also showed the same double-peak pattern that had been observed by Vela 4.〔 Although their instrumentation offered no improvement over those on Vela 5, the Vela 6 satellites were launched on April 8, 1970, with the intention of determining the direction from which the gamma rays were arriving. The orbits for the Vela 6 satellites were chosen to be as far away from Vela 5 as possible, generally on the order of 10000 kilometers apart. This separation meant that, despite gamma rays traveling at the speed of light, a signal would be detected at slightly different times by different satellites. By analyzing the arrival times, Klebesadel and his team successfully traced sixteen gamma-ray bursts. The random distribution of bursts across the sky made it clear that the bursts were not coming from the sun, moon, or other planets in our solar system.〔 In 1973, Ray Klebesadel, Roy Olson, and Ian Strong of the University of California Los Alamos Scientific Laboratory published ''Observations of Gamma-Ray Bursts of Cosmic Origin'', identifying a cosmic source for the previously unexplained observations of gamma-rays.〔 Shortly thereafter, Klebesadel presented his findings at the 140th meeting of the American Astronomical Society. Although he was interviewed only by ''The National Enquirer'', news of the discovery quickly spread through the scientific community.〔Schilling 2002, p.16–17〕 Between 1973 and 2001 more than 5300 papers were published on GRBs.〔Hurley 2003〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「History of gamma-ray burst research」の詳細全文を読む スポンサード リンク
|