Soft-gamma repeaters

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The first soft-gamma repeater was discovered on March 5, 1979 when gamma ray detectors on nine spacecraft across our solar system recorded an intense radiation spike (Mazets et al. 1979). The burst of gamma rays originated from near a supernova remnant known as N49 in the Large Magellanic Cloud. The tail of the gamma-ray burst exhibited an eight-second pulsation (in contrast with the classical gamma-ray bursts which show no periodicities). If one combined this eight-second period with the age of the supernova remnant and assumed that the ob ject (presumably a neutron star) was born spinning much faster, one estimated a magnetic field on the ob ject of ∼ 1015 G, much larger than any neutron star discovered up to that point. This first SGR became known as SGR 0526-66. During 1979, two others were discovered: SGR 1806-20 (27 December 2004 event), SGR 1900+14 (28 August 1998 event) (Mazets et al. 1981). In 1998 SGR 1627-41 became the fourth SGR to be discovered (Woods et al. 1999). Thompson & Duncan (1995, 1996) argued that the evolution of a ultrastrong magnetic field could explain both the outbursts and quiescent emission from soft-gamma repeaters, and the term “magnetar” was born. They argued earlier that if protoneutron star was born spinning sufficiently rapidly, a dynamo could dramatically amplify the standard pulsar magnetic field (∼ 1012 G) that the protoneutron star was born with to ∼ 1015 G or more Thompson & Duncan (1993).