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GRB 970228〔"GRB" indicates that the event was a gamma-ray burst, and the numbers follow a YYMMDD format corresponding to the date on which the burst occurred: 28 February 1997.〕 was the first gamma-ray burst (GRB) for which an afterglow was observed.〔Schilling 2002, p. 101〕 It was detected on 28 February 1997 at 02:58 UTC. Since 1993, physicists had predicted GRBs to be followed by a lower-energy afterglow (in wavelengths such as radio waves, x-rays, and even visible light), but until this event, GRBs had only been observed in highly luminous bursts of high-energy gamma rays (the most energetic form of electromagnetic radiation). The burst had multiple peaks in its light curve and lasted approximately 80 seconds. Peculiarities in the light curve of GRB 970228 suggested that a supernova may have occurred as well. The position of the burst coincided with a galaxy about 8.1 billion light-years〔 away (a redshift of z = 0.695), providing early evidence that GRBs occur well beyond the Milky Way. == Observations == 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.〔Schilling 2002, pp. 12–16〕 GRB 970228〔 was detected on 28 February 1997 at 02:58 UTC by the Gamma-Ray Burst Monitor (GRBM) and one of the Wide Field Cameras (WFCs) on board BeppoSAX,〔Varendoff 2001, p. 381〕〔Costa 1997b〕 an Italian–Dutch satellite originally designed to study X-rays.〔Schilling 2002, pp. 58–60〕 Within a few hours, the BeppoSAX team determined the burst's position with an error box—a small area around the specific position to account for the error in the position—of 3 arcminutes.〔 The burst was also detected by the Ulysses space probe.〔Hurley 1997〕 The burst was located at a right ascension of and a declination of in optical images taken with the William Herschel Telescope on La Palma, providing the first arcsecond-accuracy localization of any Gamma-ray burst.〔 It lasted around 80 seconds and had multiple peaks in its light curve.〔Costa 1997a〕 Gamma-ray bursts have very diverse time profiles, and it is not fully understood why some bursts have multiple peaks and some have only one. One possible explanation is that multiple peaks are formed when the source of the gamma-ray burst undergoes precession.〔Zwart 2001〕 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 970228」の詳細全文を読む スポンサード リンク
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