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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 disks 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|url=http://adsabs.harvard.edu/abs/2000ApJ...545L.127Z|accessdate=22 August 2016|bibcode=2000ApJ...545L.127Z|doi=10.1086/317889|arxiv = astro-ph/0010225 }}</ref>
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 disks 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|url=http://adsabs.harvard.edu/abs/2000ApJ...545L.127Z|accessdate=22 August 2016|bibcode=2000ApJ...545L.127Z|doi=10.1086/317889|arxiv = astro-ph/0010225 }}</ref>


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 | accessdate=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 | accessdate=March 2, 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/>
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 | accessdate=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 | accessdate=March 2, 2009 | deadurl=yes | archiveurl=https://web.archive.org/web/20090311072756/http://science.msfc.nasa.gov/newhome/headlines/ast20may98_1.htm | archivedate=March 11, 2009 | df= }}</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.
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.
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==External links==
==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}}
*{{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 |deadurl=yes |archiveurl=https://web.archive.org/web/20130517180957/http://solomon.as.utexas.edu/~duncan/magnetar.html |archivedate=2013-05-17 |df= }}
* [http://fits.nrao.edu/pr/1998/magnetar/background/ NRAO, ''Cosmic Flasher Reveals All!'']
* [https://archive.is/20110720014214/http://fits.nrao.edu/pr/1998/magnetar/background/ NRAO, ''Cosmic Flasher Reveals All!'']
* [http://hera.ph1.uni-koeln.de/~heintzma/magnetar/All_magnetars.htm H. Heintzmann, ''Happy birthday, Magnetars'', March 5, 1999.]
* [https://www.webcitation.org/6JFHS0fjt?url=http://hera.ph1.uni-koeln.de/~heintzma/magnetar/All_magnetars.htm H. Heintzmann, ''Happy birthday, Magnetars'', March 5, 1999.]


{{Neutron star}}
{{Neutron star}}

Revision as of 20:17, 22 January 2018

A soft gamma repeater (SGR) is an astronomical object which emits large bursts of gamma-rays and X-rays at irregular intervals. It is conjectured that they are a type of magnetar or, alternatively, neutron stars with fossil disks around them.[1]

On March 5, 1979[2] a powerful gamma-ray burst was noted. As a number of receivers at different locations in the Solar System[3] 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.[2][3]

Over time it became clear that this was not a normal gamma-ray burst. The photons 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 theory that soft gamma repeaters were magnetars.[2][3] According to the theory, the bursts would cause the object to slow down its rotation. In 1998,[2][3] 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 strength of 8×1010 teslas (8×1014 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 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.

Known soft gamma repeaters include:[4]

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[5] 2008 Rotates once every 2.07 seconds, holds the record for the fastest-spinning magnetar.
SGR 0501+4516 [6] 2008 Distance 15,000 light-years; X-ray outburst detected by Swift satellite 22 August 2008.
PSR J1745-2900 2013 A soft gamma repeater orbiting the black hole in Sagittarius A*

The numbers give the position in the sky, for example, SGR 0525-66 has a right ascension of 5h25m and a declination of −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

  1. ^ Zhang, Bing; Xu, R.X.; Qiao, G.J. (2000). "Nature and Nurture: a Model for Soft Gamma-Ray Repeaters". The Astrophysical Journal. 545 (2): 127–129. arXiv:astro-ph/0010225. Bibcode:2000ApJ...545L.127Z. doi:10.1086/317889. Retrieved 22 August 2016.
  2. ^ a b c d Duncan, Robert C. (May 1998). "The March 5th Event". Magnetars', Soft Gamma Repeaters & Very Strong Magnetic Fields. University of Texas at Austin. Retrieved March 2, 2009.
  3. ^ a b c d Dooling, Dave (May 20, 1998). ""Magnetar" discovery solves 19-year-old mystery". NASA. Archived from the original on March 11, 2009. Retrieved March 2, 2009. {{cite web}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  4. ^ "McGill SGR/AXP Online Catalog".
  5. ^ "Star Emits Intense Celestial Fireworks". Space.com. 10 February 2009.
  6. ^ "Giant eruption reveals 'dead' star". European Space Agency. 16 June 2009. Retrieved 28 December 2009.

Further reading

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