Editing Soft gamma repeater

{{short description|Astronomical object which emits bursts of gamma or x-rays at irregular intervals}}
{{More citations needed|date=February 2025}}
A '''soft gamma repeater''' ('''SGR''') is an [[astronomy|astronomical]] object which emits large bursts of [[gamma-ray]]s and [[X-ray]]s at irregular intervals. It is conjectured that they are a type of [[magnetar]] or, alternatively, [[neutron star]]s with fossil [[Accretion disk|disk]]s around them.<ref>{{cite journal|last1=Zhang|first1=Bing|last2=Xu|first2=R.X.|last3=Qiao|first3=G.J.|title=Nature and Nurture: a Model for Soft Gamma-Ray Repeaters|journal=The Astrophysical Journal|date=2000|volume=545|issue=2|pages=127–129|bibcode=2000ApJ...545L.127Z|doi=10.1086/317889|arxiv = astro-ph/0010225 |s2cid=14745312}}</ref>

==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.

==List of SGR==
Known soft gamma repeaters include:<ref name=McGillCatalog>{{cite web| url=http://www.physics.mcgill.ca/~pulsar/magnetar/main.html|title=McGill SGR/AXP Online Catalog}}</ref>
{| class="wikitable"
|-
! Object !! Discovery !! Notes
|-
| [[SGR 0525−66]] ||1979 ||
|-
| [[SGR 1806−20]] ||1979/1986 ||The most powerful soft gamma repeater burst yet recorded was observed coming from this object on December 27, 2004.
|-
| [[SGR 1900+14]] ||1979/1986 || 20,000 lyr away; powerful, affected the [[Earth's atmosphere]].
|-
| [[SGR 1627−41]] ||1998 ||
|-
| [[SGR J1550−5418]]<ref>{{cite web |url=http://www.space.com/scienceastronomy/090210-celestial-fireworks.html |title=Star Emits Intense Celestial Fireworks |date=10 February 2009 |publisher=[[Space.com]]}}</ref> || 2008 || Rotates once every 2.07 seconds, holds the record for the fastest-spinning [[magnetar]].
|-
| [[SGR 0501+4516]]<ref name="esa16609">{{cite web|url=http://www.esa.int/esaSC/SEMLEDQORVF_index_0.html|title=Giant eruption reveals 'dead' star|date=16 June 2009|publisher=[[European Space Agency]]|access-date=28 December 2009}}</ref> ||2008 || 15,000 lyr away; X-ray outburst detected by [[Swift Gamma-Ray Burst Mission|Swift]] satellite 22 August 2008.
|-
| [[SGR J1745−2900]] || 2013 || A soft gamma repeater orbiting the [[black hole]] in [[Sagittarius A*]].
|-
| [[SGR 1935+2154]] || 2014 || 30,000 lyr away; First ever detected [[fast radio burst]] inside the Milky Way, and the first ever to be linked to a known source.
|}

The numbers give the position in the sky, for example, SGR 0525-66 has a [[right ascension]] of 5h25m and a [[declination]] of &minus;66°. The date of discovery sometimes appears in a format such as 1979/1986 to refer to the year the object was discovered, in addition to the year soft gamma repeaters were recognized as a separate class of objects rather than "normal" gamma-ray bursts.

==References==
{{Reflist}}

==Further reading== <!-- future refs -->
*[https://arxiv.org/abs/astro-ph/9612091 On the persistent X-ray emission from the soft gamma-ray repeaters. Usov. 1996]

==External links==
* {{cite web |url= http://solomon.as.utexas.edu/~duncan/magnetar.html |title= 'Magnetars', Soft Gamma Repeaters & Very Strong Magnetic Fields |first= Robert C. |last= Duncan |location= University of Texas |url-status= dead |archive-url=https://web.archive.org/web/20130517180957/http://solomon.as.utexas.edu/~duncan/magnetar.html |archive-date= May 17, 2013 }}
* {{cite web |url = http://fits.nrao.edu/pr/1998/magnetar/background |title= Cosmic Flasher Reveals All! |publisher= [[National Radio Astronomy Observatory|NRAO]] |archive-date= July 20, 2011 |archive-url= https://web.archive.org/web/20110720014214/http://fits.nrao.edu/pr/1998/magnetar/background }}
* {{cite web |url= http://hera.ph1.uni-koeln.de/~heintzma/magnetar/All_magnetars.htm |first= H. |last= Heintzmann |title= Happy birthday, Magnetars |date= Mar 5, 1999 |quote= Scientists note 20th anniversary of March 5, 1979 gamma-ray burst event |url-status= dead |archive-date= February 27, 2012 |archive-url= https://web.archive.org/web/20120227075606/http://hera.ph1.uni-koeln.de/~heintzma/magnetar/All_magnetars.htm }}

{{Neutron star}}

[[Category:Soft gamma repeaters| ]]
[[Category:Star types]]
[[Category:Astronomical events]]