scholarly journals RESONANT SWITCH MODEL OF HF QPOS AND EQUATIONS OF STATE OF NEUTRON STARS AND QUARK STARS

2014 ◽  
Vol 54 (5) ◽  
pp. 363-366
Author(s):  
Zdenek Stuchlík ◽  
Martin Urbanec ◽  
Andrea Kotrlová ◽  
Gabriel Török ◽  
Katerina Goluchová
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
High Frequency ◽  
Equations Of State ◽  
Rotational Frequency ◽  
Periodic Oscillations ◽  
Star Models ◽  
Quark Stars ◽  
Resonant Switch ◽  
Best Fit

The mass and spin estimates of the 4U 1636−53 neutron star obtained by the Resonant Switch (RS) model of high-frequency quasi-periodic oscillations (HF QPOs) are tested by a large variety of equations of state (EoS) governing the structure of neutron stars. Neutron star models are constructed under the Hartle–Thorne theory of slowly rotating neutron stars calculated using the observationally given rotational frequency<em> f</em><sub>rot</sub> = 580 Hz (or alternatively <em>f</em><sub>rot</sub> = 290 Hz) of the neutron star at 4U 1636−53. It is demonstrated that only two variants of the RS model are compatible with the parameters obtained by modelling neutron stars for the rotational frequency <em>f</em><sub>rot</sub> = 580 Hz. The variant giving the best fit with parameters M ~ 2.20M<sub>ʘ</sub> and <em>a</em> ~ 0.27 agrees with high precision with the prediction of one of the Skyrme EoS [1]. The variant giving the second best fit with parameters M ~ 2.12M<sub>ʘ</sub> and <em>a</em> ~ 0.20 agrees with lower precision with the prediction of the Gandolfi EoS [2].

scholarly journals Restrictions to neutron star models based on twin-peak quasi-periodic oscillations

2012 ◽  
Vol 8 (S291) ◽  
pp. 524-526
Author(s):  
Gabriel Török ◽  
Martin Urbanec ◽  
Kateřina Goluchová ◽  
Pavel Bakala ◽  
Eva Šrámková ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Equations Of State ◽  
Periodic Oscillations ◽  
Star Models ◽  
Twin Peak

AbstractIn a series of works - Török et al. (2010, 2012a) and Urbanec et al. (2010a) - we explored restrictions to neutron star properties that are implied by various models of twin-peak quasi-periodic oscillations. Here we sketch an attempt to confront the obtained mass–angular-momentum relations and limits on neutron star compactness with the parameters estimated by assuming various equations of state and the spin frequency of the atoll source 4U 1636-53.

scholarly journals The Maximum Moment of Inertia of Neutron Stars and its Implications for Pulsar Observations

1992 ◽  
Vol 128 ◽  
pp. 217-219
Author(s):  
Pawel Haensel
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Approximate Formula ◽  
Equations Of State ◽  
Dense Matter ◽  
Moment Of Inertia ◽  
Observational Constraints ◽  
Maximum Moment ◽  
Star Models ◽  
Precise Representation

AbstractA simple approximate formula, expressing the maximum moment of inertia of a neutron star as a function of the mass and radius of the configuration with a maximum allowable mass, is shown to be a quite precise representation of the results obtained for a broad set of equations of state of dense matter. The resulting possible observational constraints in the mass-radius plane for neutron star models are discussed.

scholarly journals Resonant switch model of twin peak HF QPOs applied to the atoll source 4U 1636-53

2012 ◽  
Vol 8 (S290) ◽  
pp. 317-318
Author(s):  
Zdeněk Stuchlík ◽  
Andrea Kotrlová ◽  
Gabriel Török
Keyword(s):  
Neutron Star ◽  
High Frequency ◽  
Specific Model ◽  
Periodic Oscillations ◽  
Non Linear ◽  
Resonant Switch ◽  
Frequency Ratios ◽  
Twin Peak ◽  
Resonant Point ◽  
Resonant Phenomena

AbstractWe present a Resonant Switch (RS) model of twin peak high-frequency quasi-periodic oscillations (HF QPOs), assuming switch of twin oscillations at a resonant point, where frequencies of the upper and lower oscillations νU and νL become to be commensurable and the twin oscillations change from one pair of the oscillating modes (corresponding to a specific model of HF QPOs) to some other pair due to non-linear resonant phenomena. The RS model enables to determine range of allowed values of spin a and mass M of the neutron star located at the atoll source 4U 1636-53 where two resonant points are observed at frequency ratios νU : νL = 3:2, 5:4.

scholarly journals Neutron star structure in the presence of conformally coupled scalar fields

2014 ◽  
Vol 23 (11) ◽  
pp. 1450090 ◽  
Author(s):  
Joseph Sultana ◽  
Benjamin Bose ◽  
Demosthenes Kazanas
Keyword(s):  
Neutron Star ◽  
Scalar Field ◽  
Neutron Stars ◽  
Equations Of State ◽  
Complete Solution ◽  
Scalar Fields ◽  
Star Models ◽  
Neutron Star Mass ◽  
Theories Of Gravity ◽  
Star Structure

Neutron star models are studied in the context of scalar–tensor theories of gravity in the presence of a conformally coupled scalar field, using two different numerical equations of state (EoS) representing different degrees of stiffness. In both cases we obtain a complete solution by matching the interior numerical solution of the coupled Einstein-scalar field hydrostatic equations, with an exact metric on the surface of the star. These are then used to find the effect of the scalar field and its coupling to geometry, on the neutron star structure, particularly the maximum neutron star mass and radius. We show that in the presence of a conformally coupled scalar field, neutron stars are less dense and have smaller masses and radii than their counterparts in the minimally coupled case, and the effect increases with the magnitude of the scalar field at the center of the star.

scholarly journals Estimation of Electrical Conductivity and Magnetization Parameter of Neutron Star Crusts and Applied to the High-Braking-Index Pulsar PSR J1640-4631

Universe ◽  
2020 ◽  
Vol 6 (5) ◽  
pp. 63
Author(s):  
Hui Wang ◽  
Zhi-Fu Gao ◽  
Huan-Yu Jia ◽  
Na Wang ◽  
Xiang-Dong Li
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
General Expression ◽  
Equations Of State ◽  
Rotation Period ◽  
Ohmic Dissipation ◽  
Hartree Fock ◽  
Induction Equation ◽  
The Magnetic Field

Young pulsars are thought to be highly magnetized neutron stars (NSs). The crustal magnetic field of a NS usually decays at different timescales in the forms of Hall drift and Ohmic dissipation. The magnetization parameter ω B τ is defined as the ratio of the Ohmic timescale τ O h m to the Hall drift timescale τ H a l l . During the first several million years, the inner temperature of the newly born neutron star cools from T = 10 9 K to T = 1.0 × 10 8 K, and the crustal conductivity increases by three orders of magnitude. In this work, we adopt a unified equations of state for cold non-accreting neutron stars with the Hartree–Fock–Bogoliubov method, developed by Pearson et al. (2018), and choose two fiducial dipole magnetic fields of B = 1.0 × 10 13 G and B = 1.0 × 10 14 G, four different temperatures, T, and two different impurity concentration parameters, Q, and then calculate the conductivity of the inner crust of NSs and give a general expression of magnetization parameter for young pulsars: ω B τ ≃ ( 1 − 50 ) B 0 / ( 10 13 G) by using numerical simulations. It was found when B ≤ 10 15 G, due to the quantum effects, the conductivity increases slightly with the increase in the magnetic field, the enhanced magnetic field has a small effect on the matter in the low-density regions of the crust, and almost has no influence the matter in the high-density regions. Then, we apply the general expression of the magnetization parameter to the high braking-index pulsar PSR J1640-4631. By combining the observed arrival time parameters of PSR J1640-4631 with the magnetic induction equation, we estimated the initial rotation period P 0 , the initial dipole magnetic field B 0 , the Ohm dissipation timescale τ O h m and Hall drift timescale τ H a l l . We model the magnetic field evolution and the braking-index evolution of the pulsar and compare the results with its observations. It is expected that the results of this paper can be applied to more young pulsars.

scholarly journals Dynamical Stability of Neutron Stars

1971 ◽  
Vol 46 ◽  
pp. 341-345
Author(s):  
G. Chanmugam ◽  
M. Gabriel
Keyword(s):  
Neutron Star ◽  
Equation Of State ◽  
Neutron Stars ◽  
Dynamical Stability ◽  
Star Models

The Nemeth-Sprung equation of state is modified and used to obtain neutron star models. Contrary to the results of some authors it is found that neutron stars with central densities ≲ 1014 g cm-3 are dynamically stable. It is suggested that some pulsars may belong to this category of stars.

scholarly journals CONSTRAINING MODELS OF TWIN-PEAK QUASI-PERIODIC OSCILLATIONS WITH REALISTIC NEUTRON STAR EQUATIONS OF STATE

2016 ◽  
Vol 833 (2) ◽  
pp. 273 ◽  
Author(s):  
Gabriel Török ◽  
Kateřina Goluchová ◽  
Martin Urbanec ◽  
Eva Šrámková ◽  
Karel Adámek ◽  
...  
Keyword(s):  
Neutron Star ◽  
Equations Of State ◽  
Periodic Oscillations ◽  
Twin Peak

scholarly journals Einstein Observatory Limits on Neutron Star Surface Temperatures

1987 ◽  
Vol 125 ◽  
pp. 457-457
Author(s):  
F.R. Harnden
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Neutron Stars ◽  
Supernova Remnants ◽  
Theoretical Models ◽  
X Ray ◽  
Star Models ◽  
Formation And Evolution ◽  
Star Surface ◽  
Einstein Observatory

For years the theoretical models of neutron star formation and evolution had remained largely unconstrained by observation. Following the Einstein X-ray Observatory surveys of supernova remnants and pulsars, however, strict temperature limits were placed on many putative neutron stars. The Einstein search for additional objects in the class of supernova remnants with embedded pulsars has increased the number of such objects by two. For the four objects in this class, the surface temperature limits (see Table 1) provide meaningful logically sound constraints on the neutron star models. For the future, however, still better X-ray observations are needed, both to increase the number of objects available for study and to refine the spatial and spectral capabilities of the X-ray measurements.

scholarly journals Accretion onto Magnetized Neutron Stars: Polar Cap Flow and Centrifugally Driven Winds

1987 ◽  
Vol 125 ◽  
pp. 207-225
Author(s):  
Jonathan Arons
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Neutron Stars ◽  
Orbital Evolution ◽  
Time Dependent ◽  
Polar Cap ◽  
Periodic Oscillations ◽  
X Ray ◽  
Polar Caps ◽  
Basic Concepts

Some basic concepts of accretion onto the polar caps of magnetized neutron stars are reviewed. Preliminary results of new, multidimensional, time–dependent calculations of polar cap flow are outlined, and are used to suggest the possible observability of fluctuations in the X–ray intensity of accretion powered pulsars on time scales of 10–100 msec. The possible relevance of such fluctuations to Quasi–Periodic oscillations is suggested. Basic concepts of the interaction between a disk and the magnetosphere of a neutron star are also discussed. Some recent work on the disk–magnetosphere interaction is outlined, leading to the suggestion that a neutron star can lose angular momentum by driving some or all of the mass in the disk off as a centrifugally driven wind. The relevance of such mass loss to the orbital evolution of the binary is pointed out.

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