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Journal ArticleDOI

The strongest cosmic magnets: soft gamma-ray repeaters and anomalous X-ray pulsars

Sandro Mereghetti1
08 Jul 2008-The Astronomy and Astrophysics Review (Springer-Verlag)-Vol. 15, Iss: 4, pp 225-287
Abstract: Two classes of X-ray pulsars, the anomalous X-ray pulsars and the soft gamma-ray repeaters, have been recognized in the last decade as the most promising candidates for being magnetars: isolated neutron stars powered by magnetic energy. I review the observational properties of these objects, focussing on the most recent results, and their interpretation in the magnetar model. Alternative explanations, in particular those based on accretion from residual disks, are also considered. The possible relations between these sources and other classes of neutron stars and astrophysical objects are also discussed.
Citations
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Journal ArticleDOI
TL;DR: In this paper, the authors present a catalog of the 26 currently known magnetars and magnetar candidates, and investigate and plot possible correlations between their timing, X-ray, and multiwavelength properties.
Abstract: We present a catalog of the 26 currently known magnetars and magnetar candidates. We tabulate astrometric and timing data for all catalog sources, as well as their observed radiative properties, particularly the spectral parameters of the quiescent X-ray emission. We show histograms of the spatial and timing properties of the magnetars, comparing them with the known pulsar population, and we investigate and plot possible correlations between their timing, X-ray, and multiwavelength properties. We find the scale height of magnetars to be in the range 20–31pc, assuming they are exponentially distributed. This range is smaller than that measured for OB stars, providing evidence that magnetars are born from the most massive O stars. From the same fits, we find that the Sun lies ∼13–22pc above the Galactic plane, consistent with previous measurements. We confirm previously identified correlations between quiescent X-ray luminosity LX and magnetic field B, as well as X-ray spectral power-law index and B, and show evidence for an excluded region in a plot of LX vs. . We also present an updated kT versus characteristic age plot, showing magnetars and high-B radio pulsars are hotter than lower-B neutron stars of similar age. Finally, we observe a striking difference between magnetars detected in the the hard X-ray and radio bands; there is a clear correlation between the hard and soft X-ray flux, whereas the radio-detected magnetars all have low soft X-ray flux suggesting, if anything, that the two bands are anti-correlated. An online version of the catalog is located at http://www.physics.mcgill.ca/~pulsar/magnetar/main.html.

638 citations

Journal ArticleDOI
TL;DR: In this paper, a rotating magnetar radiating according to the classic dipole formula could power a very luminous supernova and the peak luminosity would be most sensitive to the dipole field strength of the magnetar.
Abstract: Following an initial explosion that might be launched either by magnetic interactions or neutrinos, a rotating magnetar radiating according to the classic dipole formula could power a very luminous supernova. While some 56Ni might be produced in the initial explosion, the peak of the light curve in a Type I supernova would not be directly related to its mass. In fact, the peak luminosity would be most sensitive to the dipole field strength of the magnetar. The tail of the light curve could resemble radioactive decay for some time but, assuming complete trapping of the pulsar emission, would eventually be brighter. Depending on the initial explosion energy, both high and moderate velocities could accompany a very luminous light curve.

478 citations

Journal ArticleDOI
TL;DR: In this paper, the main effects of propagation from cosmologically distant sources, including interactions with cosmic background radiation and magnetic fields, are discussed, leading to a survey of candidate sources and their signatures.
Abstract: The origin of the highest energy cosmic rays is still unknown. The discovery of their sources is expected to reveal the workings of the most energetic astrophysical accelerators in the Universe. Current observations show a spectrum consistent with an origin in extragalactic astrophysical sources. Candidate sources range from the birth of compact objects to explosions related to gamma-ray bursts or to events in active galaxies. We discuss the main effects of propagation from cosmologically distant sources, including interactions with cosmic background radiation and magnetic fields. We examine possible acceleration mechanisms leading to a survey of candidate sources and their signatures. New questions arise from an observed hint of sky anisotropies and an unexpected evolution of composition indicators. Future observations may reach the necessary sensitivity to achieve charged particle astronomy and to observe ultrahigh-energy photons and neutrinos, which may further illuminate the workings of the Universe a...

471 citations

Journal ArticleDOI
TL;DR: In this paper, the authors present a catalog of the 26 currently known magnetars and magnetar candidates, and investigate and plot possible correlations between their timing, X-ray, and multiwavelength properties.
Abstract: We present a catalog of the 26 currently known magnetars and magnetar candidates. We tabulate astrometric and timing data for all catalog sources, as well as their observed radiative properties, particularly the spectral parameters of the quiescent X-ray emission. We show histograms of the spatial and timing properties of the magnetars, comparing them with the known pulsar population, and we investigate and plot possible correlations between their timing, X-ray, and multiwavelength properties. We find the scale height of magnetars to be in the range 20-31 pc, assuming they are exponentially distributed. This range is smaller than that measured for OB stars, providing evidence that magnetars are born from the most massive O stars. From the same fits, we find that the Sun lies ~13-22 pc above the Galactic plane, consistent with previous measurements. We confirm previously identified correlations between quiescent X-ray luminosity L_X and magnetic field B, as well as X-ray spectral power-law index Gamma and B, and show evidence for an excluded region in a plot of L_X vs. Gamma. We also present an updated kT versus characteristic age plot, showing magnetars and high-B radio pulsars are hotter than lower-B neutron stars of similar age. Finally, we observe a striking difference between magnetars detected in the the hard X-ray and radio bands; there is a clear correlation between the hard and soft X-ray flux, whereas the radio-detected magnetars all have low soft X-ray flux suggesting, if anything, that the two bands are anti-correlated. An online version of the catalog is located at this http URL

455 citations


Cites background or methods from "The strongest cosmic magnets: soft ..."

  • ...…requires amendment because as discussed in this work and extensively elsewhere (e.g. Gavriil et al. 2002; Kaspi et al. 2003; Woods & Thompson 2006; Mereghetti 2008; Kaspi 2010; Mereghetti 2013; Rea & Esposito 2011) the distinction between sources designated as “AXP” and “SGRs” has been largely…...

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  • ...Several authors have written important review papers on magnetars, their observational properties, and outstanding questions in the field; (see Woods & Thompson 2006; Mereghetti 2008; Kaspi 2010; Rea & Esposito 2011; Mereghetti 2013)....

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Journal ArticleDOI
TL;DR: In this article, the authors present the results of 2D simulations of the fully-coupled evolution of temperature and magnetic field in neutron stars, including the state-of-the-art kinetic coefficients and, for the first time, the important effect of the Hall term.
Abstract: Observations of magnetars and some of the high magnetic field pulsars have shown that their thermal luminosity is systematically higher than that of classical radiopulsars, thus confirming the idea that magnetic fields are involved in their X-ray emission. Here we present the results of 2D simulations of the fully-coupled evolution of temperature and magnetic field in neutron stars, including the state-of-the-art kinetic coefficients and, for the first time, the important effect of the Hall term. After gathering and thoroughly re-analysing in a consistent way all the best available data on isolated, thermally emitting neutron stars, we compare our theoretical models to a data sample of 40 sources. We find that our evolutionary models can explain the phenomenological diversity of magnetars, high-B radio-pulsars, and isolated nearby neutron stars by only varying their initial magnetic field, mass and envelope composition. Nearly all sources appear to follow the expectations of the standard theoretical models. Finally, we discuss the expected outburst rates and the evolutionary links between different classes. Our results constitute a major step towards the grand unification of the isolated neutron star zoo.

434 citations


Cites background from "The strongest cosmic magnets: soft ..."

  • ...…long periods, and the occurrence of bursts and outbursts characteristic of Anomalous Xray Pulsars (AXPs) and Soft Gamma Repeaters (SGRs) (Mereghetti 2008), are interpreted as different facets of the restless dynamics of a strong magnetic field in these (typically) young sources, in…...

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References
More filters
Book
01 Nov 2010
TL;DR: A decade of X-ray sources and their evolution is described in this paper, with a focus on the formation and evolution of super-soft sources and the formation of compact stellar sources.
Abstract: 1. Accreting neutron stars and black holes: a decade of discoveries D. Psaltis 2. Rapid X-ray variability M. van der Klis 3. New views of thermonuclear bursts T. Strohmayer and L. Bildsten 4. Black hole binaries J. McClintock and R. Remillard 5. Optical, ultraviolet and infrared observations of X-ray binaries P. Charles and M. Coe 6. Fast X-ray transients and X-ray flashes J. Heise and J. in 't Zand 7. Isolated neutron stars V. Kaspi, M. Roberts and A. Harding 8. Globular cluster X-ray sources F. Verbunt and W. Lewin 9. Jets from X-ray binaries R. Fender 10. X-Rays from cataclysmic variables E. Kuulkers, A. Norton, A. Schwope and B. Warner 11. Super soft sources P. Kahabka and E. van den Heuvel 12. Compact stellar X-ray sources in normal galaxies G. Fabbiano and N. White 13. Accretion in compact binaries A. King 14. Soft gamma repeaters and anomalous X-ray pulsars: magnetar candidates P. Woods and C. Thompson 15. Cosmic gamma-ray bursts, their afterglows, and their host galaxies K. Hurley, R. Sari and S. Djorgovski 16. Formation and evolution of compact stellar X-ray sources T. Tauris and E. van den Heuvel.

3,100 citations

Journal ArticleDOI
TL;DR: In this article, it is argued that a convective dynamo can also generate a very strong dipole field after the merger of a neutron star binary, but only if the merged star survives for as long as about 10-100 ms.
Abstract: It is proposed that the main observational signature of magnetars, high-field neutron stars, is gamma-ray bursts powered by their vast reservoirs of magnetic energy. If they acquire large recoils, most magnetars are unbound from the Galaxy or reside in an extended, weakly bound Galactic corona. There is evidence that the soft gamma repeaters are young magnetars. It is argued that a convective dynamo can also generate a very strong dipole field after the merger of a neutron star binary, but only if the merged star survives for as long as about 10-100 ms. Several mechanisms which could impart a large recoil to these stars at birth, sufficient to escape from the Galactic disk, are discussed.

2,482 citations

Journal ArticleDOI

1,537 citations


"The strongest cosmic magnets: soft ..." refers background in this paper

  • ...Since the tail emission is thought to originate from the fraction of the energy released in the initial spike that remains trapped in the neutron star magnetosphere, forming an optically thick photon-pair plasma (Thompson and Duncan 1995), this indicates that the magnetic field in the three sources is similar....

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Journal ArticleDOI
TL;DR: In this article, the decay rate of the core field is a very strong function of temperature and therefore of the magnetic flux density, which is not present in the decay of the weaker fields associated with ordinary radio pulsars.
Abstract: We calculate the quiescent X-ray, neutrino, and Alfven wave emission from a neutron star with a very strong magnetic field, Bdipole ~ 1014 − 1015 G and Binterior ~ (5–10) × 1015 G. These results are compared with observations of quiescent emission from the soft gamma repeaters and from a small class of anomalous X-ray pulsars that we have previously identified with such objects. The magnetic field, rather than rotation, provides the main source of free energy, and the decaying field is capable of powering the quiescent X-ray emission and particle emission observed from these sources. New features that are not present in the decay of the weaker fields associated with ordinary radio pulsars include fracturing of the neutron star crust, strong heating of its core, and effective suppression of thermal conduction perpendicular to the magnetic field. As the magnetic field is forced through the crust by diffusive motions in the core, multiple small-scale fractures are excited, as well as a few large fractures that can power soft gamma repeater bursts. The decay rate of the core field is a very strong function of temperature and therefore of the magnetic flux density. The strongest prediction of the model is that these sources will show no optical emissions associated with X-ray heating of an accretion disk.

1,128 citations

Journal ArticleDOI
21 May 1998-Nature
TL;DR: In this paper, the authors reported the discovery of pulsations in the persistent X-ray flux of SGR1806-20, with a period of 7.47 s and a spindown rate of 2.6 x 10(exp -3) s/yr.
Abstract: Soft gamma-ray repeaters (SGRs) emit multiple, brief (approximately O.1 s) intense outbursts of low-energy gamma-rays. They are extremely rare; three are known in our galaxy and one in the Large Magellanic Cloud. Two SGRs are associated with young supernova remnants (SNRs), and therefore most probably with neutron stars, but it remains a puzzle why SGRs are so different from 'normal' radio pulsars. Here we report the discovery of pulsations in the persistent X-ray flux of SGR1806-20, with a period of 7.47 s and a spindown rate of 2.6 x 10(exp -3) s/yr. We argue that the spindown is due to magnetic dipole emission and find that the pulsar age and (dipolar) magnetic field strength are approximately 1500 years and 8 x 10(exp 14) gauss, respectively. Our observations demonstrate the existence of 'magnetars', neutron stars with magnetic fields about 100 times stronger than those of radio pulsars, and support earlier suggestions that SGR bursts are caused by neutron-star 'crust-quakes' produced by magnetic stresses. The 'magnetar' birth rate is about one per millenium, a substantial fraction of that of radio pulsars. Thus our results may explain why some SNRs have no radio pulsars.

980 citations