Bayesian timing analysis of giant flare of SGR  180620 by RXTE PCA

Hambaryan, V.; Neuhäuser, R.; Kokkotas, Kostas D.

doi:10.1051/0004-6361/201015273

Cited by 28 publications

(35 citation statements)

References 31 publications

(54 reference statements)

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“…As first pointed out by Sotani et al (2008a), the interpretation of the frequencies 30, 92 and 150 Hz in SGR 1806−20 in terms of the , and QPOs is very tempting. Here we note that the 18 Hz oscillation may be interpreted as the first edge QPO , which for model APR+DH has a frequency of about Hz (this could also correspond to the frequency at 16.9 Hz found by Hambaryan et al 2011). Similarly, the 36.4 Hz oscillation could be interpreted as the QPO.…”

Section: Summary and Discussionsupporting

confidence: 69%

Magnetoelastic oscillations of neutron stars with dipolar magnetic fields

Gabler

Cerdá–Durán

Stergioulas

et al. 2012

Monthly Notices of the Royal Astronomical Society

174

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By means of two‐dimensional, general relativistic magnetohydrodynamical simulations we investigate the oscillations of magnetized neutron star models (magnetars) for one particular dipolar magnetic field configuration including the description of an extended solid crust. The aim of this study is to understand the origin of the quasi‐periodic oscillations (QPOs) observed in the giant flares of soft gamma‐ray repeaters (SGRs). We confirm our previous findings which showed the existence of three different regimes in the evolution depending on the magnetic field strength: (a) a weak magnetic field regime B < 5 × 1013 G, where crustal shear modes dominate the evolution; (b) a regime of intermediate magnetic fields 5 × 1013 < B < 1015 G, where Alfvén QPOs are mainly confined to the core of the neutron star and the crustal shear modes are damped very efficiently and (c) a strong field regime B > 1015 G, where magnetoelastic oscillations reach the surface and approach the behaviour of purely Alfvén QPOs. When the Alfvén QPOs are confined to the core of the neutron star, we find qualitatively similar QPOs as in the absence of a crust. The lower QPOs associated with the closed field lines of the magnetic field configuration are reproduced as in our previous simulations without crust, while the upper QPOs connected to the open field lines are displaced from the polar axis. The position of these upper QPOs strongly depends on the magnetic field strength. Additionally, we observe a family of edge QPOs and one new upper QPO, which was not previously found in the absence of a crust. We extend our semi‐analytic model to obtain estimates for the continuum of the Alfvén oscillations. Our results do not leave much room for a crustal‐mode interpretation of observed QPOs in SGR giant flares, but can accommodate an interpretation of these observations as originating from Alfvén‐like, global, turning point QPOs (which can reach the surface of the star) in models with mean surface magnetic field strengths in the narrow range of 3.8 × 1015≲B≲ 1.1 × 1016 G (for a sample of two stiff equation of state and various masses). This range is somewhat larger than estimates for magnetic field strengths in known magnetars. The discrepancy may be resolved in models including a more complicated magnetic field structure or with models taking superfluidity of the neutrons and superconductivity of the protons in the core into account.

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Section: Summary and Discussionsupporting

confidence: 69%

Magnetoelastic oscillations of neutron stars with dipolar magnetic fields

Gabler

Cerdá–Durán

Stergioulas

et al. 2012

Monthly Notices of the Royal Astronomical Society

174

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“…Three such giant bursts have been detected so far. In their afterglow, in addition to the modulation associated with the magnetar's rotation, several quasiperiodic oscillations (QPOs) in the frequency range from 18-1800 Hz were observed [8][9][10][11][12]. These oscillations have been interpreted as torsional shear modes of the crust [13].…”

Section: Frequencies Of the Fundamental Crustal Shear Modementioning

confidence: 99%

“…In this paper, I focus on shear properties of the neutron-star crusts: The shear modulus µ, shear velocities v S , and the frequency spectrum of crustal shear modes. Crustal shear modes are of particular interest for the description of quasiperiodic oscillations (QPOs) in the afterglow of giant γ-ray bursts in magnetars [8][9][10][11][12]. The shear modulus describes how the neutron-star crust elastically deforms under shear stress, i.e., it describes the stiffness of the crust lattice under shear deformations.…”

Section: Introductionmentioning

confidence: 99%

Spectrum of shear modes in the neutron-star crust: Estimating the nuclear-physics uncertainties

Tews¹

2017

Phys. Rev. C

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I construct a model of the inner crust of neutron stars using interactions from chiral effective field theory (EFT) in order to calculate its equation of state (EOS), shear properties, and the spectrum of crustal shear modes. I systematically study uncertainties associated with the nuclear physics input, the crust composition, and neutron entrainment, and estimate their impact on crustal shear properties and the shear-mode spectrum. I find that the uncertainties originate mainly in two sources: The neutron-matter EOS and neutron entrainment. I compare the spectrum of crustal shear modes to observed frequencies of quasi-periodic oscillations in the afterglow of giant γ-ray bursts and find that all of these frequencies could be described within uncertainties, which are, however, at present too sizable to infer neutron-star properties from observations.

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“…Fourier amplitude at one point inside the crust r = 9.4 km and θ = 0.6. The dashed red lines indicate the frequencies of the observed QPOs during the giant flare of SGR 1806-20, the blue lines show additional frequencies found byHambaryan et al (2011), and the green line shows the frequency found in normal bursts byHuppenkothen et al (2014c). Plus (minus) signs indicate oscillations that are symmetric (antisymmetric) in Bϕ w.r.t.…”

mentioning

confidence: 99%

Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations

Gabler

Cerdá–Durán

Stergioulas

et al. 2018

Monthly Notices of the Royal Astronomical Society

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We discuss torsional oscillations of highly magnetised neutron stars (magnetars) using twodimensional, magneto-elastic-hydrodynamical simulations. Our model is able to explain both the low-and high-frequency quasi-periodic oscillations (QPOs) observed in magnetars. The analysis of these oscillations provides constraints on the breakout magnetic-field strength, on the fundamental QPO frequency, and on the frequency of a particularly excited overtone. More importantly, we show how to use this information to generically constraint properties of high-density matter in neutron stars, employing Bayesian analysis. In spite of current uncertainties and computational approximations, our model-dependent Bayesian posterior estimates for SGR 1806-20 yield a magnetic-field strengthB ∼ 2.1 +1.3 −1.0 × 10 15 G and a crust thickness of ∆r = 1.6 +0.7 −0.6 km, which are both in remarkable agreement with observational and theoretical expectations, respectively (1-σ error bars are indicated). Our posteriors also favour the presence of a superfluid phase in the core, a relatively low stellar compactness, M/R < 0.19, indicating a relatively stiff equation of state and/or low mass neutron star, and high shear speeds at the base of the crust, c s > 1.4 × 10 8 cm/s. Although the procedure laid out here still has large uncertainties, these constraints could become tighter when additional observations become available.

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Bayesian timing analysis of giant flare of SGR 180620 by RXTE PCA

Cited by 28 publications

References 31 publications

Magnetoelastic oscillations of neutron stars with dipolar magnetic fields

Magnetoelastic oscillations of neutron stars with dipolar magnetic fields

Spectrum of shear modes in the neutron-star crust: Estimating the nuclear-physics uncertainties

Constraining properties of high-density matter in neutron stars with magneto-elastic oscillations

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