Editing Soft gamma repeater (section)

==History==
On March 5, 1979<ref name=utex>{{cite web | url=http://solomon.as.utexas.edu/magnetar.html#March5 | title=The March 5th Event | last=Duncan |first=Robert C. | work=Magnetars', Soft Gamma Repeaters & Very Strong Magnetic Fields | publisher=[[University of Texas at Austin]] | date=May 1998 | access-date=March 2, 2009}}</ref> a powerful [[gamma-ray burst]] was noted. As a number of receivers at different locations in the [[Solar System]]<ref name=NASA1>{{cite web | url=http://science.msfc.nasa.gov/newhome/headlines/ast20may98_1.htm | title="Magnetar" discovery solves 19-year-old mystery | date=May 20, 1998 | publisher=[[NASA]] | last=Dooling | first=Dave | access-date=March 2, 2009 | url-status=dead | archive-url=https://web.archive.org/web/20090311072756/http://science.msfc.nasa.gov/newhome/headlines/ast20may98_1.htm | archive-date=March 11, 2009 }}</ref> saw the burst at slightly different times, its direction could be determined, and it was shown to originate from near a [[supernova remnant]] in the [[Large Magellanic Cloud]].<ref name=utex/><ref name=NASA1/>

Over time it became clear that this was not a normal gamma-ray burst. The [[photon]]s were less energetic in the soft gamma-ray and hard X-ray range, and repeated bursts came from the same region.

Astronomer [[Chryssa Kouveliotou]] of the Universities Space Research Association (USRA) at NASA's Marshall Space Flight Center decided to test the hypothesis that soft gamma repeaters were magnetars.<ref name=utex/><ref name=NASA1/> According to the hypothesis, the bursts would cause the object to slow down its rotation. In 1998,<ref name=utex/><ref name=NASA1/> she made careful comparisons of the periodicity of soft gamma repeater [[SGR 1806-20]]. The period had increased by 0.008 seconds since 1993, and she calculated that this would be explained by a magnetar with a [[magnetic field|magnetic-field]] strength of 8×10<sup>10</sup> [[Tesla (unit)|tesla]]s (8×10<sup>14</sup> [[gauss (unit)|gauss]]). This was enough to convince the international astronomical community that soft gamma repeaters are indeed magnetars.

An unusually spectacular soft gamma repeater burst was [[SGR 1900+14]] observed on August 27, 1998. Despite the large distance to this SGR, estimated at 20,000 light years, the burst had large effects on the Earth's atmosphere. The atoms in the [[ionosphere]], which are usually ionized by the Sun's radiation by day and recombine to neutral atoms by night, were ionized at nighttime at levels not much lower than the normal daytime level. The Rossi X-Ray Timing Explorer ([[RXTE]]), an [[X-ray astronomy|X-ray]] [[satellite]], received its strongest signal from this burst at this time, even though it was directed at a different part of the sky, and should normally have been shielded from the radiation.