Soft gamma repeater

Soft gamma repeater

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.

On March 5, 1979 a powerful gamma ray burst was noted. As a number of receivers at different locations in the solar system 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.

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.

The Greek astronomer Chryssa Kouveliotou decided to test the theory that soft gamma repeaters were magnetars. According to the theory, the bursts would cause the object to slow down its rotation. In 1998, 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 the 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.

As of 2000, four soft gamma repeaters are known:
* SGR 0526-66 (discovered 1979)
* SGR 1806-20 (discovered 1979/1986) — the most massive soft gamma repeater burst yet recorded was observed coming from this object on December 27, 2004.
* SGR 1900+14 (discovered 1979/1986)
* SGR 1627-41 (discovered 1998)

The numbers give the position in the sky (e.g., SGR 0526-66 has a right ascension of 5h26m 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, and the year soft gamma repeaters were recognized as a separate class of objects (rather than "normal" gamma ray bursts).

External links

* [http://www.capca.ucalgary.ca/~bniebergal/meissner/ Meissner Effect in Quark Stars] (University of Calgary)


Wikimedia Foundation. 2010.

Игры ⚽ Поможем сделать НИР

Look at other dictionaries:

  • Soft gamma repeater — Sursauteur gamma mou Un Sursauteur gamma mou, ou, en anglais, Soft gamma repeater (ou SGR) est une source astrophysique de rayons gamma connaissant des épisodes d émission violents, récurrents mais irréguliers. On pense aujourd hui qu il s agit d …   Wikipédia en Français

  • Gamma ray burst — [ GRB 990123 taken on January 23, 1999. The burst is seen as a bright dot denoted by a square on the left, with an enlarged cutout on the right. The object above it with the finger like filaments is the originating galaxy. This galaxy seems to be …   Wikipedia

  • Soft — Business* Adventure Soft, UK based video game developer which was established in the 1980s by Mike Woodroffe * Cocktail Soft, Japanese H game manufacturer * Hudson Soft, Japanese publisher and developer * Illusion Soft, company from Yokohama,… …   Wikipedia

  • Répétiteur gamma doux — Sursauteur gamma mou Un Sursauteur gamma mou, ou, en anglais, Soft gamma repeater (ou SGR) est une source astrophysique de rayons gamma connaissant des épisodes d émission violents, récurrents mais irréguliers. On pense aujourd hui qu il s agit d …   Wikipédia en Français

  • Répétiteur gamma mou — Sursauteur gamma mou Un Sursauteur gamma mou, ou, en anglais, Soft gamma repeater (ou SGR) est une source astrophysique de rayons gamma connaissant des épisodes d émission violents, récurrents mais irréguliers. On pense aujourd hui qu il s agit d …   Wikipédia en Français

  • Sursauteur gamma doux — Sursauteur gamma mou Un Sursauteur gamma mou, ou, en anglais, Soft gamma repeater (ou SGR) est une source astrophysique de rayons gamma connaissant des épisodes d émission violents, récurrents mais irréguliers. On pense aujourd hui qu il s agit d …   Wikipédia en Français

  • Sursauteur gamma mou —  Ne pas confondre avec sursaut gamma, un phénomène beaucoup plus énergétique. Un Sursauteur gamma mou, ou, en anglais, Soft gamma repeater (ou SGR) est une source astrophysique de rayons gamma connaissant des épisodes d émission violents,… …   Wikipédia en Français

  • Magnetar — For the hedge fund, see Magnetar Capital. Artist s conception of a magnetar, with magnetic field lines A magnetar is a type of neutron star with an extremely powerful magnetic field, the decay of which powers the emission of copious amounts of… …   Wikipedia

  • SGR (astronomie) — Sursauteur gamma mou Un Sursauteur gamma mou, ou, en anglais, Soft gamma repeater (ou SGR) est une source astrophysique de rayons gamma connaissant des épisodes d émission violents, récurrents mais irréguliers. On pense aujourd hui qu il s agit d …   Wikipédia en Français

  • Magnetar — künstlerische Darstellung eines Magnetars mit Feldlinien Ein Magnetar ist ein Neutronenstern, dessen Magnetfeld das 1.000 fache des bei Neutronensternen üblichen Wertes aufweist. Man schätzt, dass etwa 10 % aller Neutronensterne zu dieser… …   Deutsch Wikipedia

Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”