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GRB 970508 was a gamma-ray burst (GRB) detected on May 8, 1997, at 21:42 UTC. A gamma-ray burst is a highly luminous flash associated with an explosion in a distant galaxy and producing gamma rays, the most energetic form of electromagnetic radiation, and often followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, and radio). GRB 970508 was detected by the Gamma Ray Burst Monitor on the Italian–Dutch X-ray astronomy satellite BeppoSAX. Astronomer Mark Metzger determined that GRB 970508 occurred at least 6 billion light years from Earth; this was the first measurement of the distance to a gamma-ray burst. Until this burst, astronomers had not reached a consensus regarding how far away GRBs occur from Earth. Some supported the idea that GRBs occur within the Milky Way, but are visibly faint because they are not highly energetic. Others concluded that GRBs occur in other galaxies at cosmological distances and are extremely energetic. Although the possibility of multiple types of GRBs meant that the two theories were not mutually exclusive, the distance measurement unequivocally placed the source of the GRB outside the Milky Way, effectively ending the debate. GRB 970508 was also the first burst with an observed radio frequency afterglow. By analyzing the fluctuating strength of the radio signals, astronomer Dale Frail calculated that the source of the radio waves had expanded almost at the speed of light. This provided strong evidence that GRBs are relativistically expanding explosions. ==Discovery== A gamma-ray burst (GRB) is a highly luminous flash of gamma rays—the most energetic form of electromagnetic radiation. GRBs were first detected in 1967 by the Vela satellites (a series of spacecraft designed to detect nuclear explosions in space).〔Schilling 2002, pp. 12–16〕 The initial burst is often followed by a longer-lived "afterglow" emitted at longer wavelengths (X-ray, ultraviolet, optical, infrared, and radio). The first GRB afterglow to be discovered was the X-ray afterglow of GRB 970228,〔Costa 1997〕 which was detected by BeppoSAX, an Italian–Dutch satellite originally designed to study X-rays.〔Schilling 2002, pp. 58–60〕 On Thursday May 8, 1997, at 21:42 UTC, BeppoSAX's Gamma Ray Burst Monitor registered a gamma-ray burst that lasted approximately 15 seconds.〔Pedersen 1997〕〔 It was also detected by Ulysses, a robotic space probe designed to study the Sun,〔Pian 1998〕 and by the Burst and Transient Source Experiment (BATSE) on board the Compton Gamma Ray Observatory.〔Kouveliotou 1997〕 The burst also occurred within the field of view of one of BeppoSAX's two X-ray Wide Field Cameras. Within a few hours, the BeppoSAX team localized the burst to an error box—a small area around the specific position to account for the error in the position—with a diameter of approximately 10 arcminutes.〔Schilling 2002, pp. 115–116〕 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「GRB 970508」の詳細全文を読む スポンサード リンク
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