Strong toroidal magnetic fields sustained by the elastic crust in a neutron star

Fujisawa, Kotaro; Kojima, Yasufumi; Kisaka, Shota

doi:10.1093/mnras/stac3750

Cited by 4 publications

(2 citation statements)

References 71 publications

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“…The Lorentz force is comparable in magnitude to the elastic force in the crust. However, only static magneto-elastic equilibria of the crust have been studied thus far (Kojima et al 2021(Kojima et al , 2022Fujisawa et al 2023). These studies demonstrated that neutron-star models with strong magnetic fields are possible owing to the elasticity of the crust.…”

Section: Introductionmentioning

confidence: 99%

Evolutionary Deformation toward the Elastic Limit by a Magnetic Field Confined in the Neutron-star Crust

Kojima

Kisaka

Fujisawa

2023

ApJ

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Occasional energetic outbursts and anomalous X-ray luminosities are expected to be powered by the strong magnetic field in a neutron star. For a very strong magnetic field, elastic deformation becomes excessively large such that it leads to crustal failure. We studied the evolutionary process driven by the Hall drift for a magnetic field confined inside the crust. Assuming that the elastic force acts against the Lorentz force, we examined the duration of the elastic regime and maximum elastic energy stored before the critical state. The breakup time was longer than that required for extending the field to the exterior, because the tangential components of the Lorentz force vanished in the fragile surface region. The conversion of large magnetic energy, confined to the interior, into Joule heat is considered to explain the power for central compact objects. This process can function without reaching its elastic limit, unless the magnetic energy exceeds 2 × 1047 erg, which requires an average field strength of 2 × 1015 G. Thus, the strong magnetic field hidden in the crust is unlikely to cause outbursts. Furthermore, the magnetic field configuration can discriminate between central compact objects and magnetars.

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Section: Introductionmentioning

confidence: 99%

Evolutionary Deformation toward the Elastic Limit by a Magnetic Field Confined in the Neutron-star Crust

Kojima

Kisaka

Fujisawa

2023

ApJ

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“…The Lorentz force is comparable in magnitude to the elastic force in the crust. However, only static magneto-elastic equilibria of the crust have been studied thus far (Kojima et al 2021(Kojima et al , 2022Fujisawa et al 2023). These studies demonstrated that neutron star models with strong magnetic fields are possible owing to the elasticity of the crust.…”

Section: Introductionmentioning

confidence: 99%

Evolutionary deformation toward the elastic limit by a magnetic field confined in the neutron--star crust

Kojima¹,

Kisaka²,

Fujisawa³

2023

Preprint

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Occasional energetic outbursts and anomalous X-ray luminosities are expected to be powered by the strong magnetic field in a neutron star. For a very strong magnetic field, elastic deformation becomes excessively large such that it leads to crustal failure. We studied the evolutionary process driven by the Hall drift for a magnetic field confined inside the crust. Assuming that the elastic force acts against the Lorentz force, we examined the duration of the elastic regime and maximum elastic energy stored before the critical state. The breakup time was longer than that required for extending the field to the exterior, because the tangential components of the Lorentz force vanished in the fragile surface region. The conversion of large magnetic energy, confined to the interior, into Joule heat is considered to explain the power for central compact objects. This process can function without reaching its elastic limit, unless the magnetic energy exceeds 2 × 10 47 erg, which requires an average field strength of 2 × 10 15 G. Thus, the strong magnetic field hidden in the crust is unlikely to cause outbursts. Furthermore, the magnetic field configuration can discriminate between central compact objects and magnetars.

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Observational clues to the magnetic evolution of magnetars

Makishima,

Uchida,

Enoto

2024

Monthly Notices of the Royal Astronomical Society

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Utilizing four archival X-ray datasets taken with the Hard X-ray Detector onboard Suzaku, timing studies were performed on three magnetars, 1E 1841−045 (observed in 2006), SGR 0501+4516 (2008), and 1RXS J170849.0−400910 (2009 and 2010). Their pulsations were reconfirmed, typically in an energy range of 12–50 keV. The 11.783 s pulses of 1E 1841−045 and those of SGR 0501+4516 at 5.762 s were periodically phase modulated, with a long period of ≈23.4 ks and ≈16.4 ks, respectively. The pulse-phase modulation was also observed, at ≈46.5 ks, from two datasets of 1RXS J170849.0−400910. In all these cases, the modulation amplitude was 6 to 16% of the pulse cycle. Including previously confirmed four objects, this characteristic timing behavior is now detected from seven magnetars in total, and interpreted as a result of free precession of neutron stars that are deformed to an asphericity of ∼10−4. Assuming that the deformation is due to magnetic stress, these magnetars are inferred to harbor toroidal magnetic fields of Bt ∼ 1016 G. By comparing the estimated Bt of these objects with their poloidal dipole field Bd, the Bt/Bd ratio is found to increase with their characteristic age. Therefore, the toroidal fields of magnetars are likely to last longer than their poloidal fields. This explains the presence of some classes of neutron stars that have relatively weak Bd but are suspected to hide strong Bt inside them.

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Strong toroidal magnetic fields sustained by the elastic crust in a neutron star

Cited by 4 publications

References 71 publications

Evolutionary Deformation toward the Elastic Limit by a Magnetic Field Confined in the Neutron-star Crust

Evolutionary Deformation toward the Elastic Limit by a Magnetic Field Confined in the Neutron-star Crust

Evolutionary deformation toward the elastic limit by a magnetic field confined in the neutron--star crust

Observational clues to the magnetic evolution of magnetars

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