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TOPIC: Anomalous X-ray Pulsars


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magnetar XTE J1810-197
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A team of scientists, including astronomers from CSIRO in Australia, have discovered a neutron star which is giving off extraordinary radio pulses.
The neutron star is called XTE J1810-197 and lies about 10 000 light-years away in the constellation Sagittarius.
It's emitting radio pulses at every turn of the star, or every 5.54 seconds.
This animation gives an artist's impression of the star, but the audio is real, recorded by CSIRO scientists at the Parkes Telescope in New South Wales.
Animation created by John Rowe Animations

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RE: Anomalous X-ray Pulsars
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Astronomers from SRON have discovered mysterious pulses that are being emitted by an extremely magnetic star. The magnetic star, a magnetar, emits the pulses as very high energy X-rays. The astronomers made their observations using the ESA space telescopes INTEGRAL and XMM-Newton and the NASA satellite RXTE.

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Posts: 131433
Date:
AXP 1E 1841-045
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Title: Suzaku Observation of AXP 1E 1841-045 in SNR Kes 73
Authors: M. Morii, S. Kitamoto, N. Shibazaki, D. Takei, N. Kawai, M. Arimoto, M. Ueno, Y. Terada, T. Kohmura, S. Yamauchi

Anomalous X-ray pulsars (AXPs) are thought to be magnetars, which are neutron stars with ultra strong magnetic field of 10^14--  10^15 G. Their energy spectra below  ~ 10 keV are modelled well by two components consisting of a blackbody (BB) ( ~ 0.4 keV) and rather steep power-law (POW) function (photon index  ~ 2-4). Kuiper et al.(2004) discovered hard X-ray component above  ~ 10 keV from some AXPs. Here, we present the Suzaku observation of the AXP 1E 1841-045 at the centre of supernova remnant Kes 73. By this observation, we could analyse the spectrum from 0.4 to 50 keV at the same time. Then, we could test whether the spectral model above was valid or not in this wide energy range. We found that there were residual in the spectral fits when fit by the model of BB + POW. Fits were improved by adding another BB or POW component. But the meaning of each component became ambiguous in the phase-resolved spectroscopy. Alternatively we found that NPEX model fit well for both phase-averaged spectrum and phase-resolved spectra. In this case, the photon indices were constant during all phase, and spectral variation seemed to be very clear. This fact suggests somewhat fundamental meaning for the emission from magnetars.

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RE: Anomalous X-ray Pulsars
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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.

 Source: European Space Agency

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Posts: 131433
Date:
XTE J1810-197
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Some neutron stars have such powerful magnetic fields that they rip themselves open due to magnetic forces, a new study confirms.
A neutron star is the dense core left behind when a massive star explodes as a supernova. Made of subatomic particles called neutrons, the stars are so dense that a teaspoonful of their material would weigh 500 million tonnes.
The spins of some neutron stars decrease rapidly, suggesting they boast extremely powerful magnetic fields that radiate electromagnetic energy that slows their rotation. This type of neutron star is called a magnetar.
But it was always possible that the neutron stars might be slowing down for other reasons, for example as a result of spewing charged particles out into space.
Now, new observations of a candidate magnetar have confirmed that it has a magnetic field 600 trillion times the strength of Earth's field powerful enough to explain the 'starquake' it experienced in 2003. The study team was led by Tolga Guver of Istanbul University in Turkey.

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Posts: 131433
Date:
Permalink  
 

ESAs 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 magnetars 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.

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Posts: 131433
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Magnetars
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Title: On the corona of magnetars
Authors: Yury Lyubarsky, David Eichler

Slow dissipation of non-potential magnetic fields in the magnetosphere of the magnetar is assumed to accelerate particles to hundreds MeV along the magnetic field lines. We consider interaction of fast particles with the surface of the magnetar. We argue that the collisionless dissipation does not work in the atmosphere of the neutron star because the two-stream instability is stabilized by the inhomogeneity of the atmosphere. Rather, the dominant dissipation mechanism is collisional Landau levelexcitations followed by pair production via the deexcitation gamma-rays ultimately leading to electrons with the energy below the Landau energy. We show that, because of the effects of the superstrong magnetic field, these electrons could emerge from the surface carrying most of the original energy so that a hot corona arises with the temperature of 1 - 2 MeV. This extended corona is better suited than a thin atmosphere to convert most of the primary beam energy to non-thermal radiation and, as we show, most of the coronal energy release is radiated away in the hard X-ray and the soft gamma-ray bands by Comptonization and bremsstrahlung. The radiation spectrum is a power-law with the photon index 1<\alpha<2. The model may account for the persistent hard X-ray emission discovered recently from the soft gamma-ray repeaters and anomalous X-ray pulsars and predicts that the radiation spectrum is extended into the MeV band.

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Posts: 131433
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RE: Anomalous X-ray Pulsars
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Title: AXPs/SGRs: Magnetars or Quark-stars?
Authors: Renxin Xu (PKU)
(Version v5)

The magnetar model and a solid quark star model for anomalous X-ray pulsars/soft gamma-ray repeaters (AXPs/SGRs) are discussed. Different manifestations of pulsar-like stars are speculated to be due to both their nature (e.g., mass and strain) and their nurture (ambience, and consequently the type of accretion) in the solid quark star scenario. Relevant arguments made by the author's group, including a debate on solid cold quark matter, are briefly summarised too.

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Posts: 131433
Date:
Magnetar Westerlund 1
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Magnetars are among the rarest objects in the universe, and the oddest.
The collapsed remnants of enormous stars, they have a magnetic field about a million-billion times as strong as Earth's. Though they weigh more than 300,000 times as much as our planet, they are only about 12 miles across.
Astronomers have only discovered 13 magnetars.
It was a stroke of luck, then, that Caltech astrophysicist Michael Muno happened to be watching when the Westerlund 1 magnetar experienced a sudden "star quake."

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Posts: 131433
Date:
magnetar XTE J1810-197
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Title: VLBA measurement of the transverse velocity of the magnetar XTE J1810-197
Authors: D. J. Helfand (1), S. Chatterjee (2), W. F. Brisken (3), F. Camilo (1), J. Reynolds (4), M. H. van Kerkwijk (5), J. P. Halpern (1), S. M. Ransom (3) ((1) Columbia U., (2) U. of Sydney, (3) NRAO, (4) ATNF, (5) U. of Toronto)

We have obtained observations of the magnetar XTE J1810-197 with the Very Long Baseline Array at two epochs separated by 106 days, at wavelengths of 6 cm and 3.6 cm. Comparison of the positions yields a proper motion value of 13.5 ±1.0 mas/yr at an equatorial position angle of 209.4 ±2.4 deg (east of north). This value is consistent with a lower-significance proper motion value derived from infrared observations of the source over the past three years, also reported here. Given its distance of 3.5 ±0.5 kpc, the implied transverse velocity corrected to the local standard of rest is 212 ±35 km/s (1 sigma). The measured velocity is slightly below the average for normal young neutron stars, indicating that the mechanism(s) of magnetar birth need not lead to high neutron star velocities. We also use Australia Telescope Compact Array, Very Large Array, and these VLBA observations to set limits on any diffuse emission associated with the source on a variety of spatial scales, concluding that the radio emission from XTE J1810-197 is >96% pulsed.

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