Atmospheres and radiating surfaces of neutron stars

The magnetic dipole radiation (MDR) model is currently the best approach we have to explain pulsar radiation. However a most characteristic parameter of the observed radiation, the braking index n obs shows deviations for all the eight best studied isolated pulsars, from the simple model prediction n dip = 3. The index depends upon the rotational frequency and its first and second time derivatives, but also on the assumption of that the magnetic dipole moment and inclination angle, and the moment of inertia of the pulsar are constant in time. In a recent paper [Phys. Rev. D 91, 063007 (2015)] we showed conclusively that changes in the moment of inertia with frequency alone, cannot explain the observed braking indices.Possible observational evidence for the magnetic dipole moment migrating away from the rotational axis at a rateα ∼ 0.6 • per 100 years over the life time of the Crab pulsar has been recently suggested by Lyne et al. In this paper, we explore the MDR model with constant moment of inertia and magnetic dipole moment but variable inclination angle α. We first discuss the effect of the variation of α on the observed braking indices and show they all can be understood. However, no explanation for the origin of the change in α is provided.After discussion of the possible source(s) of magnetism in pulsars we propose a simple mechanism for the change in α based on a toy model in which the magnetic structure in pulsars consists of two interacting dipoles. We show that such a system can explain the Crab observation and the measured braking indices.

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“…There is extensive literature on this subject, documenting the complexity of the problem (see e.g. [20,21,23] ).…”

Section: Mechanisms Of Pulsar Magnetismmentioning

confidence: 99%

Braking index of isolated pulsars. II. A novel two-dipole model of pulsar magnetism

Hamil

Stone

2016

Phys. Rev. D

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“…(see [47] and references there). Atmospheres of accreting NSs have the same mixture of elements as the donor star if the accretion rate is much faster than the process of gravitational separation.…”

Section: Chemical Compositionmentioning

confidence: 99%

Measuring the basic parameters of neutron stars using model atmospheres

et al. 2016

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Abstract. Model spectra of neutron star atmospheres are nowadays widely used to fit the observed thermal X-ray spectra of neutron stars. This fitting is the key element in the method of the neutron star radius determination. Here, we present the basic assumptions used for the neutron star atmosphere modeling as well as the main qualitative features of the stellar atmospheres leading to the deviations of the emergent model spectrum from blackbody. We describe the properties of two of our model atmosphere grids: (i) pure carbon atmospheres for relatively cool neutron stars (1-4 MK) and (ii) hot atmospheres with Compton scattering taken into account. The results obtained by applying these grids to model the X-ray spectra of the central compact object in supernova remnant HESS 1731−347, and two X-ray bursting neutron stars in low-mass X-ray binaries, 4U 1724−307 and 4U 1608−52, are presented. Possible systematic uncertainties associated with the obtained neutron star radii are discussed.

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“…However, the determination of the radius of a NS is subject to many assumptions, uncertainties and systematics effects, (see e.g. table 1 in [8]). Obtaining constraints from the PRE bursts of BNS is still subject to uncertainties and debates in particular concerning the modelling of the phenomenon itself, the selection of bursts to be used (hard state X-ray bursts vs. soft state ones) and the composition of the atmosphere (see [12][13][14][15][16][17]).…”

Section: Radiusmentioning

confidence: 99%

“…The radius of a NS can in principle be extracted from the analysis of X-ray spectra emitted by the NS atmosphere (see [8] for a review). However even in the case of a nonrotating NS, due to the space-time curvature, only the apparent radius,…”

Section: Radiusmentioning

confidence: 99%

Rotating neutron stars with exotic cores: masses, radii, stability

Haensel¹,

Bejger²,

Fortin³

et al. 2016

Eur. Phys. J. A

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Abstract.A set of theoretical mass-radius relations for rigidly rotating neutron stars with exotic cores, obtained in various theories of dense matter, is reviewed. Two basic observational constraints are used: the largest measured rotation frequency (716 Hz) and the maximum measured mass (2M ). The present status of measuring the radii of neutron stars is described. The theory of rigidly rotating stars in general relativity is reviewed and limitations of the slow rotation approximation are pointed out. Mass-radius relations for rotating neutron stars with hyperon and quark cores are illustrated using several models. Problems related to the non-uniqueness of the crust-core matching are mentioned. Limits on rigid rotation resulting from the mass-shedding instability and the instability with respect to the axisymmetric perturbations are summarized. The problem of instabilities and of the back-bending phenomenon are discussed in detail. Metastability and instability of a neutron star core in the case of a first-order phase transition, both between pure phases, and into a mixed-phase state, are reviewed. The case of two disjoint families (branches) of rotating neutron stars is discussed and generic features of neutron-star families and of core-quakes triggered by the instabilities are considered.

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Atmospheres and radiating surfaces of neutron stars

Cited by 121 publications

References 387 publications

Braking index of isolated pulsars. II. A novel two-dipole model of pulsar magnetism

Braking index of isolated pulsars. II. A novel two-dipole model of pulsar magnetism

Measuring the basic parameters of neutron stars using model atmospheres

Rotating neutron stars with exotic cores: masses, radii, stability

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