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Journal Article•DOI•

Electrodynamics of Magnetars: Implications for the Persistent X-ray Emission and Spindown of the Soft Gamma Repeaters and Anomalous X-ray Pulsars

C. Thompson, Maxim Lyutikov1, Shri Kulkarni2•
McGill University1, California Institute of Technology2
31 Oct 2001-arXiv: Astrophysics-
TL;DR: In this paper, the authors considered the structure of neutron star magnetospheres threaded by large-scale electrical currents and the effect of resonant Compton scattering by the charge carriers (both electrons and ions) on the emergent X-ray spectra and pulse profiles.
Abstract: (ABBREVIATED) We consider the structure of neutron star magnetospheres threaded by large-scale electrical currents, and the effect of resonant Compton scattering by the charge carriers (both electrons and ions) on the emergent X-ray spectra and pulse profiles. In the magnetar model for the SGRs and AXPs, these currents are maintained by magnetic stresses acting deep inside the star. We construct self-similar, force-free equilibria of the current-carrying magnetosphere with a power-law dependence of magnetic field on radius, B ~ r^(-2-p), and show that a large-scale twist softens the radial dependence to p < 1. The spindown torque acting on the star is thereby increased in comparison with a vacuum dipole. We comment on the strength of the surface magnetic field in the SGR and AXP sources, and the implications of this model for the narrow measured distribution of spin periods. A magnetosphere with a strong twist, B_\phi/B_\theta = O(1) at the equator, has an optical depth ~ 1 to resonant cyclotron scattering, independent of frequency (radius), surface magnetic field strength, or charge/mass ratio of the scattering charge. When electrons and ions supply the current, the stellar surface is also heated by the impacting charges at a rate comparable to the observed X-ray output of the SGR and AXP sources, if B_{dipole} ~ 10^{14} G. Redistribution of the emerging X-ray flux at the ion and electron cyclotron resonances will significantly modify the emerging pulse profile and, through the Doppler effect, generate a non-thermal tail to the X-ray spectrum. The sudden change in the pulse profile of SGR 1900+14 after the 27 August 1998 giant flare is related to an enhanced optical depth to electron cyclotron scattering, resulting from a sudden twist imparted to the external magnetic field.
Citations
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Journal Article•DOI•
The evolution and structure of pulsar wind nebulae

[...]

Bryan Gaensler1, Patrick Slane1•
Harvard University1
18 Aug 2006-Annual Review of Astronomy and Astrophysics
TL;DR: In this article, the authors describe how pulsars steadily dissipate their rotational energy via relativistic winds. Confinement of these outflows generates luminous pulsar wind nebulae, seen across the electromagnetic spectrum in...
Abstract: Pulsars steadily dissipate their rotational energy via relativistic winds. Confinement of these outflows generates luminous pulsar wind nebulae, seen across the electromagnetic spectrum in ...

771 citations

Journal Article•DOI•
The strongest cosmic magnets: soft gamma-ray repeaters and anomalous X-ray pulsars

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Sandro Mereghetti1•
INAF1
08 Jul 2008-The Astronomy and Astrophysics Review
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.

751 citations

Journal Article•DOI•
Physics of strongly magnetized neutron stars

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Alice K. Harding1, Dong Lai2•
Goddard Space Flight Center1, Cornell University2
23 Aug 2006-Reports on Progress in Physics
TL;DR: In this paper, the exotic physics of high magnetic field regime was discussed, where a new array of processes becomes possible and even dominant and where familiar processes acquire unusual properties, including free particles, atoms, molecules, plasma and condensed matter in strong magnetic fields, photon propagation in magnetized plasmas, freeparticle radiative processes, the physics of neutron star interiors and field evolution and decay mechanisms.
Abstract: There has recently been growing evidence for the existence of neutron stars possessing magnetic fields with strengths that exceed the quantum critical field strength of 4.4 × 1013 G, at which the cyclotron energy equals the electron rest mass. Such evidence has been provided by new discoveries of radio pulsars having very high spin-down rates and by observations of bursting gamma-ray sources termed magnetars. This paper will discuss the exotic physics of this high-field regime, where a new array of processes becomes possible and even dominant and where familiar processes acquire unusual properties. We review the physical processes that are important in neutron star interiors and magnetospheres, including the behaviour of free particles, atoms, molecules, plasma and condensed matter in strong magnetic fields, photon propagation in magnetized plasmas, free-particle radiative processes, the physics of neutron star interiors and field evolution and decay mechanisms. Application of such processes in astrophysical source models, including rotation-powered pulsars, soft gamma-ray repeaters, anomalous x-ray pulsars and accreting x-ray pulsars will also be discussed. Throughout this review, we will highlight the observational signatures of high magnetic field processes, as well as the theoretical issues that remain to be understood.

740 citations

Cites background from "Electrodynamics of Magnetars: Impli..."

  • ...…a corona consisting mainly of relativistic electron-positron pairs can be generated by crustal magnetic field twisting/shearing due to starquakes, with the plasma density much higher (by a factor of order c/Ωr) than the Goldreich-Julian value (Thompson et al. 2002; Thompson & Beloborodov 2005)....

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  • ...The field line twists following starquakes (and the associated X-ray burst activities) may last for years and lead to significant heating of the near vicinity of the star (Thompson et al. 2002; Thompson & Beloborodov 2005)....

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Journal Article•DOI•
The mcgill magnetar catalog

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S. A. Olausen1, Victoria M. Kaspi1•
McGill University1
17 Apr 2014-Astrophysical Journal Supplement Series
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 Article•DOI•
An exceptionally bright flare from SGR 1806–20 and the origins of short-duration γ-ray bursts

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Kevin Hurley1, Steven E. Boggs2, Steven E. Boggs1, David M. Smith3, Robert C. Duncan4, Robert P. Lin1, Andreas Zoglauer1, Säm Krucker1, G. J. Hurford1, Hugh S. Hudson1, C. Wigger5, Wojtek Hajdas5, Christopher Thompson, I. G. Mitrofanov, A. B. Sanin, William V. Boynton6, C. Fellows6, A. von Kienlin5, G. G. Lichti5, Arne Rau5, T. L. Cline7 •
Space Sciences Laboratory1, University of California, Berkeley2, Santa Cruz Institute for Particle Physics3, University of Texas at Austin4, Max Planck Society5, University of Arizona6, Goddard Space Flight Center7
28 Apr 2005-Nature
TL;DR: In this article, the authors reported the detection of a long (380's) giant flare from SGR 1806-20, which was much more luminous than any previous transient event observed in our Galaxy.
Abstract: Soft-γ-ray repeaters (SGRs) are galactic X-ray stars that emit numerous short-duration (about 0.1 s) bursts of hard X-rays during sporadic active periods. They are thought to be magnetars: strongly magnetized neutron stars with emissions powered by the dissipation of magnetic energy. Here we report the detection of a long (380 s) giant flare from SGR 1806–20, which was much more luminous than any previous transient event observed in our Galaxy. (In the first 0.2 s, the flare released as much energy as the Sun radiates in a quarter of a million years.) Its power can be explained by a catastrophic instability involving global crust failure and magnetic reconnection on a magnetar, with possible large-scale untwisting of magnetic field lines outside the star. From a great distance this event would appear to be a short-duration, hard-spectrum cosmic γ-ray burst. At least a significant fraction of the mysterious short-duration γ-ray bursts may therefore come from extragalactic magnetars. On 27 December last year, SGR1806–20, a soft γ-ray repeater in Sagittarius, released a giant flare that has been called the brightest explosion ever recorded. SGRs are X-ray stars that sporadically emit low-energy γ-ray bursts. They are thought to be magnetars: neutron stars with observable emissions powered by magnetic dissipation. Five papers in this issue report initial and follow-up observations of this event. The data are remarkable: for instance in a fifth of a second, the flare released as much energy as the Sun radiates in a quarter of a million years. Such power can be explained by catastrophic global crust failure and magnetic reconnection on a magnetar. Releasing a hundred times the energy of the only two previous SGR giant flares, this may have been a once-in-a-lifetime event for astronomers, and for the star itself.

590 citations

References
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Journal Article•DOI•
Formation of very strongly magnetized neutron stars - Implications for gamma-ray bursts

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Robert C. Duncan, Christopher Thompson
10 Jun 1992-The Astrophysical Journal
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

"Electrodynamics of Magnetars: Impli..." refers background in this paper

  • ...These objects where hypothesized to form through dynamo action in supernova collapse (Duncan & Thompson 1992)....

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  • ...…supply enough energy to power the bursts, thereby matching the extreme peak luminosities of more a million times Eddington; and to confine a significant proportion of the cooling plasma over the long (> 200 s) duration of the flare (Duncan & Thompson 1992; Pacyzński 1992; Thompson & Duncan 1995)....

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  • ...A neutron star is generically formed with strong differential rotation (because its equation of state is stiff), and will support a large-scale helical dynamo when its initial spin period is shorter than the convective overturn time of ∼ 3− 10 ms (Duncan & Thompson 1992)....

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  • ...…young, convective neutron stars: a large-scale helical dynamo is possible when the initial spin period is shorter than ∼ 3 msec (the convective overturn time of nuclear matter from which neutrinos are escaping with a luminosity Lν ∼> 1052 erg s−1) (Duncan & Thompson 1992; Thompson & Duncan 1993)....

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Journal Article•DOI•
Theory of pulsars: polar gaps, sparks, and coherent microwave radiation

[...]

Ruderman, P.G. Sutherland
15 Feb 1975-The Astrophysical Journal

1,927 citations

Journal Article•DOI•
The soft gamma repeaters as very strongly magnetized neutron stars - I. Radiative mechanism for outbursts

[...]

Christopher Thompson, Robert C. Duncan1•
University of Texas at Austin1
15 Jul 1995-Monthly Notices of the Royal Astronomical Society

1,537 citations

"Electrodynamics of Magnetars: Impli..." refers background or methods in this paper

  • ...A high density of pairs can be self-consistently maintained by γ − γ collisions during an SGR burst, when the plasma temperature exceeds ∼ 30 keV (Thompson and Duncan 1995, 2001)....

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  • ...…that, further from the fireball surface, the escaping X-ray flux will become collimated along partly open magnetic field lines, as the result of the strong inequality in the scattering opacity of the two X-ray polarization modes in a super-strong magnetic field (Thompson & Duncan 1995, 2001)....

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  • ...Implications for Giant Flare Mechanism There are two generic possibilities for the production of the giant flares of the SGRs, in the framework of our model (Thompson & Duncan 1995, 2001; Woods et al. 2001a)....

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  • ...…constraints on the dipole fields of the SGR sources come from these independent lines of argument: i) Confinement of the relativistically hot plasma which powered the pulsating tails of the two giant flares requires magnetic fields stronger than 1014 (E/1044 erg)1/2 G (Thompson & Duncan 1995)....

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  • ...…supply enough energy to power the bursts, thereby matching the extreme peak luminosities of more a million times Eddington; and to confine a significant proportion of the cooling plasma over the long (> 200 s) duration of the flare (Duncan & Thompson 1992; Pacyzński 1992; Thompson & Duncan 1995)....

    [...]

Journal Article•DOI•
The Soft Gamma Repeaters as Very Strongly Magnetized Neutron Stars. II. Quiescent Neutrino, X-Ray, and Alfvén Wave Emission

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Christopher Thompson1, Christopher Thompson2, Robert C. Duncan3•
University of North Carolina at Chapel Hill1, University of Toronto2, University of Texas at Austin3
10 Dec 1996-The Astrophysical Journal
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

"Electrodynamics of Magnetars: Impli..." refers background in this paper

  • ...This striking similarity motivated the suggestion that they share a common energy source: the decay of a very strong magnetic field (Thompson & Duncan 1996, hereafter TD96)....

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Journal Article•DOI•
An X-ray pulsar with a superstrong magnetic field in the soft γ-ray repeater SGR1806 − 20

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Chryssa Kouveliotou1, Chryssa Kouveliotou2, S. Dieters3, S. Dieters2, Tod E. Strohmayer4, Tod E. Strohmayer1, J. van Paradijs3, Gerald J. Fishman2, Charles A. Meegan2, Kevin Hurley5, Jefferson M. Kommers6, Ian Smith7, Dale A. Frail, Toshio Murakami •
Universities Space Research Association1, Marshall Space Flight Center2, University of Alabama in Huntsville3, Goddard Space Flight Center4, University of California, Berkeley5, Massachusetts Institute of Technology6, Rice University7
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

"Electrodynamics of Magnetars: Impli..." refers background or result in this paper

  • ...(B11) is appropriate to the actively bursting SGRs 1806−20 and 1900+14, if they have purely dipolar magnetic fields (Kouveliotou et al. 1998, 1999)....

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  • ...…Dipole Fields of the SGRs/AXPs and their Relation to Radio Pulsar Fields The polar magnetic fields16 of the two rapidly spinning down SGRs 1806−20 and 1900+14 (Kouveliotou et al. 1998, 1999, Woods et al. 2001b) are inferred to be Bpole = 1 − 3 × 1015 G from the standard magnetic dipole formula....

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  • ...The short spindown ages of SGRs 1900+14 and 1806−20 (P/Ṗ < 3000 yrs: Kouveliotou et al. 1998, 1999; Woods et al. 2001c) seem to provide evidence, at first sight, that these sources are younger than most of the AXPs....

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  • ...The discovery of long period pulsations in the quiescent X-ray emission of SGRs by Kouveliotou et al. (1998) has opened a rich field of timing studies of SGRs (Woods et al. 1999c, 2001b; Kaspi et al. 1999, 2001; Gavriil & Kaspi 2001), from which we are now able to obtain critical information about…...

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  • ...Implications for SGR/AXP spindown The measured spindown of SGR 1806−20 (Kouveliotou et al. 1998) and SGR 1900+14 (Kouveliotou et al. 1999; Woods et al. 1999c; Marsden et al. 1999) corresponds to a polar dipole field Bpole ' 2×1015 G....

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Related Papers (5)
Electrodynamics of Magnetars: Implications for the Persistent X-Ray Emission and Spin-down of the Soft Gamma Repeaters and Anomalous X-Ray Pulsars

[...]

20 Jul 2002-The Astrophysical Journal
C. Thompson, M. Lyutikov, M. Lyutikov, Shrinivas R. Kulkarni 
The soft gamma repeaters as very strongly magnetized neutron stars - I. Radiative mechanism for outbursts

[...]

15 Jul 1995-Monthly Notices of the Royal Astronomical Society
Christopher Thompson, Robert C. Duncan
Formation of very strongly magnetized neutron stars - Implications for gamma-ray bursts

[...]

10 Jun 1992-The Astrophysical Journal
Robert C. Duncan, Christopher Thompson
The Soft Gamma Repeaters as Very Strongly Magnetized Neutron Stars. II. Quiescent Neutrino, X-Ray, and Alfvén Wave Emission

[...]

10 Dec 1996-The Astrophysical Journal
Christopher Thompson, Christopher Thompson, Robert C. Duncan
The strongest cosmic magnets: soft gamma-ray repeaters and anomalous X-ray pulsars

[...]

08 Jul 2008-The Astronomy and Astrophysics Review
Sandro Mereghetti