Soft gamma repeater

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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]

Astronomy natural science that deals with the study of celestial objects

Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics, physics, and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, moons, stars, nebulae, galaxies, and comets; the phenomena also includes supernova explosions, gamma ray bursts, quasars, blazars, pulsars, and cosmic microwave background radiation. More generally, all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, which is the study of the Universe as a whole.

X-ray form of electromagnetic radiation

X-rays make up X-radiation, a form of electromagnetic radiation. Most X-rays have a wavelength ranging from 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz (3×1016 Hz to 3×1019 Hz) and energies in the range 100 eV to 100 keV. X-ray wavelengths are shorter than those of UV rays and typically longer than those of gamma rays. In many languages, X-radiation is referred to with terms meaning Röntgen radiation, after the German scientist Wilhelm Röntgen who discovered these on November 8, 1895, who usually is credited as its discoverer, and who named it X-radiation to signify an unknown type of radiation. Spelling of X-ray(s) in the English language includes the variants x-ray(s), xray(s), and X ray(s).

Magnetar type of neutron star

A magnetar is a type of neutron star believed to have an extremely powerful magnetic field. The magnetic field decay powers the emission of high-energy electromagnetic radiation, particularly X-rays and gamma rays. The theory regarding these objects was proposed by Robert Duncan and Christopher Thompson in 1992, but the first recorded burst of gamma rays thought to have been from a magnetar had been detected on March 5, 1979. During the following decade, the magnetar hypothesis became widely accepted as a likely explanation for soft gamma repeaters (SGRs) and anomalous X-ray pulsars (AXPs).


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]

Gamma-ray burst flashes of gamma rays from distant galaxies

In gamma-ray astronomy, gamma-ray bursts (GRBs) are extremely energetic explosions that have been observed in distant galaxies. They are the brightest electromagnetic events known to occur in the universe. Bursts can last from ten milliseconds to several hours. After an initial flash of gamma rays, a longer-lived "afterglow" is usually emitted at longer wavelengths.

Solar System planetary system of the Sun

The Solar System is the gravitationally bound planetary system of the Sun and the objects that orbit it, either directly or indirectly. Of the objects that orbit the Sun directly, the largest are the eight planets, with the remainder being smaller objects, such as the five dwarf planets and small Solar System bodies. Of the objects that orbit the Sun indirectly—the moons—two are larger than the smallest planet, Mercury.

Supernova remnant remnants of an exploded star

A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar material it sweeps up and shocks along the way.

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 photon is a type of elementary particle, the quantum of the electromagnetic field including electromagnetic radiation such as light, and the force carrier for the electromagnetic force. The photon has zero rest mass and always moves at the speed of light within a vacuum.

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.

Chryssa Kouveliotou Greek astrophysicist and astronomer

Chryssa Kouveliotou is a Greek astrophysicist. She is a professor at George Washington University and a retired senior technologist in high-energy astrophysics at NASA's Marshall Space Flight Center in Huntsville, Alabama.

SGR 1806-20 star

SGR 1806-20 is a magnetar, a type of neutron star with a very powerful magnetic field, that was discovered in 1979 and identified as a soft gamma repeater. SGR 1806-20 is located about 14.5 kiloparsecs (50,000 light-years) from Earth on the far side of the Milky Way galaxy in the constellation of Sagittarius. It has a diameter of no more than 20 kilometres (12 mi) and rotates on its axis every 7.5 seconds (30,000 km/h rotation speed at the surface). As of 2016, SGR 1806-20 is the most highly magnetized object ever observed, with a magnetic field over 1015 gauss (G) (1011 tesla) in intensity (compared to the Sun's 1–5 G and Earth's 0.25–0.65 G).

Magnetic field spatial distribution of vectors allowing the calculation of the magnetic force on a test particle

A magnetic field is a vector field that describes the magnetic influence of electrical currents and magnetized materials. In everyday life, the effects of magnetic fields are often seen in permanent magnets, which pull on magnetic materials and attract or repel other magnets. Magnetic fields surround and are created by magnetized material and by moving electric charges such as those used in electromagnets. Magnetic fields exert forces on nearby moving electrical charges and torques on nearby magnets. In addition, a magnetic field that varies with location exerts a force on magnetic materials. Both the strength and direction of a magnetic field varies with location. As such, it is an example of a vector field.

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.

SGR 1900+14 gamma-ray burst

SGR 1900+14 is a soft gamma repeater (SGR), located in the constellation of Aquila about 20,000 light-years away. It is assumed to be an example of an intensely magnetic star, known as a magnetar. It is thought to have formed after a fairly recent supernova explosion.

Ionosphere The ionized part of Earths upper atmosphere

The ionosphere is the ionized part of Earth's upper atmosphere, from about 60 km (37 mi) to 1,000 km (620 mi) altitude, a region that includes the thermosphere and parts of the mesosphere and exosphere. The ionosphere is ionized by solar radiation. It plays an important role in atmospheric electricity and forms the inner edge of the magnetosphere. It has practical importance because, among other functions, it influences radio propagation to distant places on the Earth.

X-ray astronomy branch of astronomy that uses X-ray observation

X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy is the space science related to a type of space telescope that can see farther than standard light-absorption telescopes, such as the Mauna Kea Observatories, via x-ray radiation.

Known soft gamma repeaters include: [4]

SGR 0525-66 1979
SGR 1806-20 1979/1986The most powerful soft gamma repeater burst yet recorded was observed coming from this object on December 27, 2004.
SGR 1900+14 1979/198620,000 lyr away, powerful, affected the Earth's atmosphere
SGR 1627-41 1998
SGR J1550-5418 [5] 2008Rotates once every 2.07 seconds, holds the record for the fastest-spinning magnetar.
SGR 0501+4516 [6] 2008Distance 15,000 light-years; X-ray outburst detected by Swift satellite 22 August 2008.
PSR J1745-2900 2013A 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.

Right ascension Astronomical equivalent of longitude

Right ascension is the angular distance of a particular point measured eastward along the celestial equator from the Sun at the March equinox to the point above the earth in question. When paired with declination, these astronomical coordinates specify the direction of a point on the celestial sphere in the equatorial coordinate system.

Declination Astronomical coordinate analogous to latitude

In astronomy, declination is one of the two angles that locate a point on the celestial sphere in the equatorial coordinate system, the other being hour angle. Declination's angle is measured north or south of the celestial equator, along the hour circle passing through the point in question.

Related Research Articles

Neutron star degenerate stellar remnant

A neutron star is the collapsed core of a giant star which before collapse had a total of between 10 and 29 solar masses. Neutron stars are the smallest and densest stars, not counting hypothetical quark stars and strange stars. Neutron stars have a radius of the order of 10 kilometres (6.2 mi) and a mass lower than a 2.16 solar masses. They result from the supernova explosion of a massive star, combined with gravitational collapse, that compresses the core past white dwarf star density to that of atomic nuclei.

Radiation waves or particles propagating through space or through a medium, carrying energy

In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes:

Anomalous X-ray Pulsars (AXPs) are now widely believed to be magnetars—young, isolated, highly magnetized neutron stars. These energetic X-ray pulsars are characterized by slow rotation periods of ~2–12 seconds and large magnetic fields of ~1013–1015 gauss (1 to 100 gigateslas). There are currently (as of 2017) 12 confirmed and 2 candidate AXPs. The identification of AXPs with magnetars was motivated by their similarity to another enigmatic class of sources, the soft gamma repeaters.

Radio-quiet neutron star

A radio-quiet neutron star is a neutron star that does not seem to emit radio emissions, but is still visible to Earth through electromagnetic radiation at other parts of the spectrum, particularly x-rays and gamma rays.

Stellar magnetic field magnetic field generated by the motion of conductive plasma inside a star

A stellar magnetic field is a magnetic field generated by the motion of conductive plasma inside a star. This motion is created through convection, which is a form of energy transport involving the physical movement of material. A localized magnetic field exerts a force on the plasma, effectively increasing the pressure without a comparable gain in density. As a result, the magnetized region rises relative to the remainder of the plasma, until it reaches the star's photosphere. This creates starspots on the surface, and the related phenomenon of coronal loops.

Gamma-ray burst progenitors types of celestial objects

Gamma-ray burst progenitors are the types of celestial objects that can emit gamma-ray bursts (GRBs). GRBs show an extraordinary degree of diversity. They can last anywhere from a fraction of a second to many minutes. Bursts could have a single profile or oscillate wildly up and down in intensity, and their spectra are highly variable unlike other objects in space. The near complete lack of observational constraint led to a profusion of theories, including evaporating black holes, magnetic flares on white dwarfs, accretion of matter onto neutron stars, antimatter accretion, supernovae, hypernovae, and rapid extraction of rotational energy from supermassive black holes, among others.

SGR 0525-66 is a soft gamma repeater (SGR), located in the Super-Nova Remnant (SNR) 0525-66.1, otherwise known as N49, in the Large Magellanic Cloud. It was the first soft gamma repeater discovered, and as of 2015, the only known located outside our galaxy.

SGR 1900+14 gamma-ray burst

SGR 1900+14 is a soft gamma repeater (SGR), located in the constellation of Aquila about 20,000 light-years away. It is assumed to be an example of an intensely magnetic star, known as a magnetar. It is thought to have formed after a fairly recent supernova explosion.

SGR 1627-41, is a soft gamma repeater (SGR), located in the constellation of Ara. It was discovered June 15, 1998 using the Burst and transient Source Experiment (BATSE) and was the first soft gamma repeater to be discovered since 1979. During a period of 6 weeks, the star bursted approximately 100 times, and then went quiet. The measured bursts lasted an average of 100 milliseconds, but ranged from 25 ms to 1.8 seconds. AGR 1627-41 is a persistent X-ray source. It is located at a distance of 11 kpc in the radio complex CTB 33, a star forming region that includes the supernova remnant G337.0-0.1.

Gamma ray electromagnetic radiation of high frequency and therefore high energy

A gamma ray or gamma radiation, is a penetrating electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves and so imparts the highest photon energy. Paul Villard, a French chemist and physicist, discovered gamma radiation in 1900 while studying radiation emitted by radium. In 1903, Ernest Rutherford named this radiation gamma rays based on their relatively strong penetration of matter; he had previously discovered two less penetrating types of decay radiation, which he named alpha rays and beta rays in ascending order of penetrating power.

SGR J1550-5418 is a soft gamma repeater (SGR), the sixth to be discovered, located in the constellation Norma. Long known as an X-ray source, it was noticed to have become active on 23 October 2008, and then after a relatively quiescent interval, became much more active on 22 January 2009. It has been observed by the Swift satellite, and by the Fermi Gamma-ray Space Telescope, launched in 2008, as well as in X-ray and radio emission. It has been observed to emit intense bursts of gamma rays at a rate of up to several per minute. At its estimated distance of 30,000 light years, the most intense flares equal the total energy emission of the Sun in ~20 years.

Gamma-ray astronomy Observational astronomy performed with gamma rays

Gamma-ray astronomy is the astronomical observation of gamma rays, the most energetic form of electromagnetic radiation, with photon energies above 100 keV. Radiation below 100 keV is classified as X-rays and is the subject of X-ray astronomy.

SGR 0501+4516 is a soft gamma repeater (SGR), and is an ancient stellar remnant. Currently, the phenomenons of SGRs and the related Anomalous X-ray pulsars (AXP) are explained as arising from magnetars. SGR 0501+4516 is located approximately 15,000 light years from Earth and has a magnetic field 100 trillion times stronger than the Earth’s.

Astrophysical X-ray source astronomical object emitting X-rays

Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays.

SGR J1745-2900

SGR J1745−2900 or PSR J1745-2900 is the first discovered magnetar, orbiting a black hole in the Sagittarius A* system. The magnetar was discovered in 2013 using the Effelsberg 100-m Radio Telescope, the Nancay Decimetric Radio Telescope, and the Jodrell Bank Lovell Telescope. The magnetar has a period of 3.76 s and a magnetic field of ∼ 1014 G (1010 T).

GRB 790305b is an event that took place on 5 March 1979. It was an extremely bright burst that was successfully localized to supernova remnant N49 in the Large Magellanic Cloud. This event is now interpreted as a magnetar giant flare, more related to SGR flares than "true" gamma-ray bursts. It is the first observed SGR megaflare, a specific type of short GRB. It has been associated with the pulsar PSR B0525-66.

Imaging X-ray Polarimetry Explorer

The Imaging X-ray Polarimetry Explorer (IXPE) is a future space observatory with three identical telescopes designed to measure the polarization of cosmic X-rays. The mission will study exotic astronomical objects and permit mapping the magnetic fields of black holes, neutron stars, pulsars, supernova remnants, magnetars, quasars, and active galactic nuclei. The high-energy X-ray radiation from these objects' surrounding environment can be polarized – vibrating in a particular direction. Studying the polarization of X-rays reveals the physics of these objects and can provide insights into the high-temperature environments where they are created.


  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.
  2. 1 2 3 4 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. 1 2 3 4 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.
  4. "McGill SGR/AXP Online Catalog".
  5. "Star Emits Intense Celestial Fireworks". 10 February 2009.
  6. "Giant eruption reveals 'dead' star". European Space Agency. 16 June 2009. Retrieved 28 December 2009.

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