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Explosion reveals tiny magnetic island

20 September 2007

Magnetars are neutron stars with extremely powerful magnetic fields. They are extremely dense objects (the size of mountains but weighing as much as the sun), with magnetic fields hundreds of trillions of times more powerful than the Earth’s. The decay of these powerful magnetic fields powers the emission of very energetic radiation, usually in the form of X-rays or Gamma Rays

A seismic event accompanied by a powerful burst was observed on one such magnetar, Westerlund 1 in September 2005. Located in a star cluster about 15 000 light-years away in the Ara constellation in the southern hemisphere, the magnetar goes by the unwieldy official name CXOU J164710.2-455216.

Credits: NASA/Swift/Sonoma State University/A. Simonnet

ESA’s XMM-Newton, has provided new insight into puzzling celestial objects known as magnetars. Thanks to the orbiting X-ray observatory, astronomers have traced powerful explosions to a region just beneath a magnetar’s surface.

Magnetars are small neutron stars that occasionally suffer extraordinarily powerful outbursts which shine X-rays across the galaxy.

In 2003, astronomers saw a neutron star brighten to around 100 times its usual faint luminosity. This outburst allowed them to discover XTE J1810-197. Detecting pulsations from the source helped classify it as the first transient anomalous X-ray pulsar (AXP). The massive outburst moved it to the rank of magnetar.

Magnetars are perplexing objects. Each one is the highly magnetic core of a star that was once at least eight times more massive than the Sun. When it exploded as a supernova, the core was compressed into a highly compact object, a neutron star, roughly fifteen kilometres in diameter, but containing about as much mass as the Sun.

Some of these neutron stars possess the most powerful magnetic fields in the Universe, leading to extremely energetic eruptions that send high-energy radiation cascading across space. Astronomers have never been certain whether the outbursts come from the surface of the magnetar itself, or the clouds of electrically charged particles trapped in the surrounding magnetic field.

An assembly of 51 mirrors, carefully sized, formed and nested one inside another, makes XMM-Newton the most sensitive X-ray telescope ever built. ESA's XMM-Newton derives its name from its X-ray multi-mirror design and honours Sir Isaac Newton. This unique X-ray observatory was launched by Ariane 5 from the European spaceport in French Guiana on 10 December 1999.

Credits: ESA

Now, using data from XMM-Newton, Tolga Güver, Istanbul University, and his colleagues have analysed the X-ray spectrum of XTE J1810-197 using a computer model that incorporates emission from the magnetar’s surface with its subsequent processing as it travels through the object’s magnetic field. This is the first time both regions of a magnetar have been put together in the same computer model.

XMM-Newton observed XTE J1810-197 seven times between 9 August 2003 and 12 March 2006 using XMM's European Photon Imaging Camera (EPIC) on board XMM. During that time, the object faded back to normal brightness, and EPIC recorded the changes in the energies of the X-rays released as it did so. These changes are particularly valuable to astronomers because they can be compared with computer predictions.

Güver and colleagues found that the data were best fitted with a model that traced the outburst to just below the surface of the magnetar and confined it to an area about 3.5 km across. This is a breakthrough because, “Assuming our model is confirmed, we can now distinguish between surface and magnetopheric phenomena,” says Güver.

Their model also allowed them to determine the strength of this object’s magnetic field spectroscopically. It is around six hundred million, million times stronger than Earth’s magnetic field. Encouragingly, this measurement is similar to an estimate made previously for this object based on how fast its spin is slowing down. This boosts the team’s confidence that their model is correct.

Nevertheless, they are not being complacent about their work. “This model will not be the final one about magnetars but it does give us a new point of view onto these fascinating objects,” says Güver.

One thing that remains unclear is the nature of the outburst. It is probably triggered magnetically but exactly how, is still a mystery. The team now plan to use their computer model to investigate more of these celestial objects, using more data from XMM-Newton, in their quest for answers.


‘The Magnetar Nature and the Outburst Mechanism of a Transient Anomalous X-ray Pulsar’ by T. Güver, F. Özel, E. Göğüş and C. Kouveliotou is due to be published in The Astrophysical Journal, on 20 September 2007.

For more information:

Tolga Güver, Istanbul University
Email: Tolga @

Norbert Schartel, ESA XMM-Newton Project Scientist
Email: Norbert Schartel @

Source: ESA - Space Science - News

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UA Astronomers Pinpoint Origin of Nature's Most Powerful Magnetic Bursts

'Magnetar' Magnetic Field is 600 Trillion Times Stronger Than Earth's

The University of Arizona press release is reproduced below:

By Lori Stiles, University Communications
September 20, 2007

University of Arizona astronomers have pinpointed the origin of powerful bursts from nature's most magnetic objects.

The bursts are from "magnetars," some of the most enigmatic objects in the universe.

Artist's impression of the European Space Agency's
XMM-Newton Observatory. UA astronomers have used
XMM-Newton data on a "magnetar" in analyzing where
the most powerful magnetic bursts in the universe come
(Credit: ESA)

Magnetars are a type of neutron star, which are superdense stars that pack the mass of a sun into a body the size of Manhattan Island. Tiny magnetars possess magnetic fields that are at least 100 trillion times as powerful as Earth's magnetic field. They occasionally produce powerful bursts, hurling high-energy radiation cascading across space. The origin of these energetic eruptions and the strong magnetic fields is a mystery.

Astronomers discovered a magnetar with the NASA's X-Ray Timing Explorer in July 2003, when it brightened by about 100 times its usual faint luminosity. They continued monitoring it regularly with the European Photon Imaging Camera, known as EPIC, on the European Space Agency's XMM-Newton Observatory until March 2006, when the object faded to its pre-outburst brightness.

As the magnetar faded, EPIC recorded changes in the energies of the X-rays released.

This is an artistic illustration of a magnetar.
(Credit: Robert Mallozzi, NASA Marshall Space
Flight Center)

Tolga Guver, who is a visiting graduate student at the UA, working with Assistant Professor Feryal Ozel of the UA physics and UA astronomy departments, compared the magnetar's changing X-ray spectrum with predictions from a computer model. They developed the model to describe the physical properties of a magnetar's surface and magnetic field in detail.

Guver, Ozel and their collaborators found that the data was best fitted with a model that traced the outburst to just below the surface of the magnetar and confined it to an area about 3.5 kilometers (about two miles) across.

"This is the first time both the surface emission and its subsequent reprocessing in the magnetosphere have been incorporated into the same computer model," Ozel said.

"This is a breakthrough because we can now distinguish between surface and magnetospheric phenomena,'' Guver said.

Determining both the size and the location of the powerful burst is like "performing anatomy on a distant, tiny star,'' Ozel added.

Their model also allowed Guver, Ozel and their colleagues to determine spectroscopically the strength of this object's magnetic field. The magnetar's magnetic field is around 600 trillion times stronger than the Earth's magnetic field.

The scientists say they are encouraged because the measurement is similar to an earlier estimate made based on how fast the source is "spinning down," which is the change in the spin period over time. They said it boosts their confidence that their model is correct.

"It is tremendously exciting to be able to compute exotic quantum phenomena that appear only in these ultrastrong magnetic fields and to see these predictions appear in actual data,'' Ozel added.

The astronomers say that they don't yet understand the mechanism of the outburst, which is probably somehow magnetically triggered.

The researchers say they plan to use their computer model to study more magnetars, using more data from X-ray observatories, in the quest for answers.

They are publishing their results in today's edition (Sept. 20, 2007) of the Astrophysical Journal Letters. The paper's authors are Guver, Ozel, Ersin Gogus of Sabanci University, Istanbul, Turkey, and Chryssa Kouveliotou of the NASA Marshall Space Flight Center, Huntsville, Ala.

Source: UA Press Release

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