Surface of rapidly-rotating neutron stars: Implications to neutron star parameter estimation

Silva, Hector Okada da; Pappas, George; Yunes, Nicolás; Yagi, Kent

doi:10.1103/physrevd.103.063038

Cited by 21 publications

(25 citation statements)

References 77 publications

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“…Therefore, Ω2 belongs to parameters that play a crucial role in the formation of the emergent spectrum. The eccentricity of the oblate star depends on Ω2 and was obtained by the approximate (independent of the equation of state) formula from Silva et al (2021). Suleimanov et al (2020) have shown the spectra of the rotating neutron star as a function of the inclination angle and the angular velocity of the star.…”

Section: Summary and Discussionmentioning

confidence: 99%

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Influence of the gravitational darkening effect on the spectrum of a hot, rapidly rotating neutron star

Majczyna,

Madej,

Różańska

et al. 2022

Preprint

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Section: Summary and Discussionmentioning

confidence: 99%

“…The formula that connects these two variables depends on the equation of state of the matter building up neutron star. Such approximate formulae were proposed by various authors (see e.g., AlGendy & Morsink 2014;Silva et al 2021).…”

Section: Spectra Of the Rotating Neutron Starmentioning

confidence: 99%

Influence of the gravitational darkening effect on the spectrum of a hot, rapidly rotating neutron star

Majczyna,

Madej,

Różańska

et al. 2022

Preprint

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“…The oblateness parameter a can be deduced from numerical models of neutron star interiors. According to table I of Silva et al (2021), using realistic equations of state for the construc-tion of stars in stationary equilibrium for fast rotating neutron stars with frequency about 600 Hz, the ratio between polar radius R p and equatorial radius R e is about r = R p /R e ≈ 0.9, implying an oblateness parameter of a = √ r −2 − 1 ≈ 0.48. The deformation of the stellar surface is therefore substantial, leading to a slight increase in the polar cap surface area.…”

Section: Discussionmentioning

confidence: 99%

“…They also gave analytical fits to the equatorial radius. Recently Silva et al (2021) constructed equilibria configurations using realistic neutron star equations of state. Such investigations give a good estimate of the expected stellar deformation due to centrifugal forces and helps to constrain the oblateness knowing the neutron star rotation period.…”

Section: Introductionmentioning

confidence: 99%

Spheroidal force-free neutron star magnetospheres

Pétri

2021

Preprint

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Context. Fast rotating and self-gravitating astrophysical objects suffer strong deformations from centrifugal forces. If moreover they are magnetized, they generate an electromagnetic wave that is perturbed accordingly. When stellar objects are also surrounded by an ideal plasma, a magnetosphere is formed. For neutron stars, a relativistic magnetized wind is launched, efficiently extracting rotational kinetic energy flowing into particle creation and radiation. Aims. We study the electromagnetic configuration of a force-free magnetosphere encompassing an ideal spheroidal rotating conductor as an inner boundary. We put special emphasize to millisecond period neutron star magnetospheres, those showing a significant oblate shape. For completeness, we also investigate the effect of prolate stars. Methods. Force-free solutions are computed by numerical integration of the time-dependent Maxwell equations in spheroidal coordinates using pseudo-spectral techniques. Relevant quantities such as the magnetic field structure, the spin down luminosity, the polar cap rims and the current density are shown and compared to the force-free spherical star results. Results. We find that the force-free magnetic field produced by spheroidal stars remains very similar to their spherical counterpart. However, the spin down luminosity slightly decreases with increasing oblateness or prolateness. Moreover the polar cap area increases and always mostly encompasses the equivalent spherical star polar cap rims. The polar cap current density is also drastically affected. Conclusions. Neutron stars are significantly distorted by either rotational effects like millisecond pulsars or by magnetic pressure like magnetars and high-magnetic field pulsars. Observational interpretation and fitting of thermal X-ray pulsation will greatly benefit from an accurate and quantitative analyse like the one presented in this paper. However, even for the fastest possible rotation, the effect would certainly be unobservable, in the sense that we can't predict what feature of the light curve would supposedly reveal the neutron star deformation due to fast rotation.

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“…This represents a large deformation of the stellar surface. The more realistic model of Silva et al (2021) with an SLy4 equation of state would give a slightly lower value of a/R ≈ 0.48 but still large. From equation ( 81) we can then find that the spheroidal formula for the luminosity gives a correction of a factor of order 2, which is significant.…”

Section: Poynting Fluxmentioning

confidence: 96%

Spheroidal magnetic stars rotating in vacuum

Pétri

2021

Preprint

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Context. Gravity shapes stars to become almost spherical because of the isotropic nature of gravitational attraction in Newton's theory. However, several mechanisms break this isotropy like for instance their rotation generating a centrifugal force, magnetic pressure or anisotropic equations of state. The stellar surface therefore deviates slightly or significantly from a sphere depending on the strength of these anisotropic perturbations. Aims. In this paper, we compute analytical and numerical solutions of the electromagnetic field produced by a rotating spheroidal star of oblate or prolate nature. This study is particularly relevant for millisecond pulsars for which strong deformations are produced by the rotation or a strong magnetic field, leading to indirect observational signatures of the polar cap thermal X-ray emission. Methods. First we solve the time harmonic Maxwell equations in vacuum by using oblate and prolate spheroidal coordinates adapted to the stellar boundary conditions. The solutions are expanded in series of radial and angular spheroidal wave functions. Particular emphasize is put on the magnetic dipole radiation. Second, we compute approximate solutions by integrating numerically the timedependent Maxwell equations in spheroidal coordinates. Results. We show that the spin down luminosity corrections compared to a perfect sphere are to leading order given by terms involving (a/r L ) 2 and (a/R) 2 where a is the stellar oblateness or prolateness, R the smallest star radius and r L the light-cylinder radius. The corresponding perturbations in the electromagnetic field are only perceptible close to the surface, deforming the polar cap rims. At large distances r a, the solution tends asymptotically to the perfect spherical case of a rotating dipole.

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Surface of rapidly-rotating neutron stars: Implications to neutron star parameter estimation

Cited by 21 publications

References 77 publications

Influence of the gravitational darkening effect on the spectrum of a hot, rapidly rotating neutron star

Influence of the gravitational darkening effect on the spectrum of a hot, rapidly rotating neutron star

Spheroidal force-free neutron star magnetospheres

Spheroidal magnetic stars rotating in vacuum

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