Protoneutron star dynamos: pulsars, magnetars,   and 
 radio-silent X-ray emitting neutron stars

Bonanno, A.; Урпин, В. А.; Belvedère, G.

doi:10.1051/0004-6361:20054473

Cited by 49 publications

(59 citation statements)

References 15 publications

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“…We also confirm the existence of a critical spin-period, below which the dynamo is always excited independently of the differential rotation strength, and whose value is related only to the size of the neutron-finger instability zone. Since the numerical simulations show that the turbulent mean-field dynamo is very efficient in producing magnetic fields well above the equipartition value, we confirm the results of Bonanno et al (2006) even in presence of both a moving boundary of the instability zones and of an η-quenching, i.e. the proposed mechanism could represent an explanation for the large surface magnetic fields observed in several neutron stars.…”

Section: Introductionsupporting

confidence: 81%

“…The model, which includes the nonlinearities introduced by the feedback processes, which in turn tend to saturate the growth of the magnetic field, i.e. α-quenching (Bonanno et al 2005(Bonanno et al , 2006Rüdiger & Arlt 1996), and suppress its turbulent diffusion, i.e. η-quenching (Rüdiger & Arlt 1996), is evolved numerically with a very large variety of initial conditions.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic field amplification in proto-neutron stars

Naso¹,

Rezzolla

Bonanno³

et al. 2007

A&A

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Aims. During the first 40 s after their birth, proto-neutron stars are expected to be subject to at least two types of instability. The first one, the convective instability, is excited in the inner regions, where the entropy gradient produces a Rayleigh-type convection. The second one, the neutron-finger instability, is instead excited in the outer layers where the lepton gradients are large. Both instabilities involve convective motions and hence can trigger dynamo actions that may be responsible for the large magnetic fields in neutron stars and magnetars. However, because they have rather different mean turbulent velocities, they are also likely to give rise to different types of dynamo. Methods. We have solved the mean-field induction equation in a simplified one-dimensional model of both the convective and the neutron-finger instability zones. Although very idealized, the model includes the nonlinearities introduced by the feedback processes that tend to saturate the growth of the magnetic field (α-quenching) and suppress its turbulent diffusion (η-quenching). The possibility of a dynamo action is studied within a dynamical model of turbulent diffusivity where the boundary of the unstable zone is allowed to move. A large number of numerical simulations have been performed in which the relevant parameters, such as the spin-period, the strength of the differential rotation, the intensity of the initial magnetic field, and the extent of the neutron finger instability zone, have been suitably varied. Results. We show that the dynamo action can also be operative within a dynamical model of turbulent diffusivity and that the amplification of the magnetic field can still be very effective. Furthermore, we confirm the existence of a critical spin-period, below which the dynamo is always excited independently of the degree of differential rotation, and whose value is related to the size of the neutron-finger instability zone. We provide a relation for the intensity of the final field as a function of the spin of the star and of its differential rotation. Conclusions. Although they were obtained by using a toy model, we expect that our results are able to capture the qualitative and asymptotic behaviour of a mean-field dynamo action developing in the neutron-finger instability zone. Overall, we find that such a dynamo is very efficient in producing magnetic fields well above equipartition, and thus that it could represent a possible explanation for the large surface magnetic fields observed in neutron stars.

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Section: Introductionsupporting

confidence: 81%

Section: Introductionmentioning

confidence: 99%

Magnetic field amplification in proto-neutron stars

Naso¹,

Rezzolla

Bonanno³

et al. 2007

A&A

Self Cite

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“…Generally the toroidal configurations can be present in different types of stars. For instance, they are typical for the liquid cores of neutron stars (Bonanno et al 2005(Bonanno et al , 2006 where a large-scale toroidal magnetic field can be accompanied by small-scale magnetic structures (Urpin & Gil 2004).…”

Section: Introductionmentioning

confidence: 99%

Rotation and Stability of the Toroidal Magnetic Field in Stellar Radiation Zones

Bonanno

Урпин

2013

ApJ

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The stability of the magnetic field in radiation zones is of crucial importance for mixing and angular momentum transport in the stellar interior. We consider the stability properties of stars containing a predominant toroidal field in spherical geometry by means of a linear stability in the Boussinesq approximation taking into account the effect of thermal conductivity. We calculate the growth rate of instability and analyze in detail the effects of stable stratification and heat transport. We argue that the stabilizing influence of gravity can never entirely suppress the instability caused by electric currents in radiation zones. However, the stable stratification can essentially decrease the growth rate of instability.

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“…A large-scale dynamo is most efficient in the surface layers where the density gradient is highest. Therefore, the generated field increases outward and reaches its maximum in the outer layers (Bonanno et al 2005(Bonanno et al , 2006. This magnetic field can be subject to current-driven instabilities after the end of the initial phase.…”

Section: Numerical Resultsmentioning

confidence: 99%

Stability of the toroidal magnetic field in rotating stars

Bonanno

Урпин

2013

A&A

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The magnetic field in stellar radiation zones can play an important role in phenomena such as mixing, angular momentum transport, etc. We study the effect of rotation on the stability of a predominantly toroidal magnetic field in the radiation zone. In particular we considered the stability in spherical geometry by means of a linear analysis in the Boussinesq approximation. It is found that the effect of rotation on the stability depends on a magnetic configuration. If the toroidal field increases with the spherical radius, the instability cannot be suppressed entirely even by a very fast rotation. Rotation can only decrease the growth rate of instability. If the field decreases with the radius, the instability has a threshold and can be completey suppressed.

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Protoneutron star dynamos: pulsars, magnetars, and radio-silent X-ray emitting neutron stars

Cited by 49 publications

References 15 publications

Magnetic field amplification in proto-neutron stars

Magnetic field amplification in proto-neutron stars

Rotation and Stability of the Toroidal Magnetic Field in Stellar Radiation Zones

Stability of the toroidal magnetic field in rotating stars

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