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 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 Restrictions to Neutron Star Properties Based on Twin-Peak Quasi-Periodic Oscillations

2012 ◽  
Vol 8 (S290) ◽  
pp. 319-320
Author(s):  
Gabriel Török ◽  
Pavel Bakala ◽  
Eva Šrámková ◽  
Zdeněk Stuchlík ◽  
Martin Urbanec ◽  
...  
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
High Frequency ◽  
Low Frequency ◽  
Periodic Oscillations ◽  
Specific Relation ◽  
Low Mass ◽  
Twin Peak

AbstractWe consider twin-peak quasi-periodic oscillations (QPOs) observed in the accreting low-mass neutron star (NS) binaries and explore restrictions to NS properties that are implied by various QPO models. For each model and each source, the consideration results in a specific relation between the NS mass M and the angular-momentum j rather than in their single preferred combination. Furthermore, the inferred restrictions on NS properties (or QPO models) are weaker for the low-frequency sources than for the high-frequency sources.

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 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.

scholarly journals SOME EFFECTS OF NUCLEAR FORCES ON NEUTRON-STAR MODELS

1966 ◽  
Vol 44 (8) ◽  
pp. 1895-1922 ◽  
Author(s):  
Sachiko Tsuruta ◽  
A. G. W. Cameron
Keyword(s):  
Neutron Star ◽  
Equations Of State ◽  
The Other ◽  
Central Density ◽  
Stable Configuration ◽  
Nuclear Forces ◽  
Solar Mass ◽  
Star Models ◽  
Repulsive Forces ◽  
Lack Of Knowledge

Two composite equations of state have been used in the investigation of the structure of neutron (or hyperon or baryon) stars. These have been based upon two forms of the neutron–neutron potential suggested by Levinger and Simmons. In one form, repulsive forces come in quickly at greater than nuclear densities, while, in the other form, the repulsive forces come in slowly. In the former case the maximum stable mass of a neutron star is about two solar masses, whereas in the latter case it is only about one solar mass. This probably represents a measure of the basic uncertainty in the properties of neutron-star models due to our lack of knowledge of nuclear forces. The maximum central density of a stable configuration is similarly uncertain; this density probably lies in the range 1015 to 1016 g/cm3. Details of many of the neutron-star models calculated are summarized and discussed.

NUMERICAL METHODS FOR SOLVING THE RELATIVISTIC OPPENHEIMER–VOLKOFF EQUATIONS

2007 ◽  
Vol 18 (11) ◽  
pp. 1735-1746 ◽  
Author(s):  
P. J. PAPASOTIRIOU ◽  
V. S. GEROYANNIS ◽  
S. A. SANIDAS
Keyword(s):  
Neutron Star ◽  
Numerical Methods ◽  
Equations Of State ◽  
Hydrostatic Equilibrium ◽  
Step Method ◽  
Star Models ◽  
Systems Of Differential Equations ◽  
Straightforward Method ◽  
Variable Step ◽  
Independent Variable

In this paper, three methods for computing non-rotating neutron star models are discussed. The relativistic Oppenheimer–Volkoff (OV) equations of hydrostatic equilibrium are solved using (a) the well-known variable step method, (b) a method based on a modified form of the OV equations, where the thermodynamic enthalpy function is the independent variable, and (c) a new straightforward method, based on the ODEPACK Fortran package for solving systems of differential equations. We present results concerning several equations of state and conclusions concerning the applicability of each method.

scholarly journals Hadron Star Models

1974 ◽  
Vol 53 ◽  
pp. 237-250
Author(s):  
Jeffrey M. Cohen ◽  
Gerhard Börner
Keyword(s):  
Star Formation ◽  
Neutron Star ◽  
Equations Of State ◽  
Binding Energies ◽  
Star Models

The properties of fully relativistic rotating hadron star models are discussed using models based on recently developed equations of state. All of these stable neutron star models are bound with binding energies as high as ∼ 25%. During hadron star formation, much of this energy will be released. The consequences, resulting from the release of this energy, are examined.

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 Kilohertz quasi-periodic oscillations from neutron star spreading layers

2020 ◽  
Vol 638 ◽  
pp. A142
Author(s):  
Pavel Abolmasov ◽  
Joonas Nättilä ◽  
Juri Poutanen
Keyword(s):  
Angular Momentum ◽  
Neutron Star ◽  
Axial Symmetry ◽  
Light Curves ◽  
Periodic Oscillations ◽  
Radial Extent ◽  
Accretion Rates ◽  
Inclination Angles ◽  
Low Mass ◽  
X Ray Binaries

When the accretion disc around a weakly magnetised neutron star (NS) meets the stellar surface, it should brake down to match the rotation of the NS, forming a boundary layer. As the mechanisms potentially responsible for this braking are apparently inefficient, it is reasonable to consider this layer as a spreading layer (SL) with negligible radial extent and structure. We perform hydrodynamical 2D spectral simulations of an SL, considering the disc as a source of matter and angular momentum. Interaction of new, rapidly rotating matter with the pre-existing, relatively slow material co-rotating with the star leads to instabilities capable of transferring angular momentum and creating variability on dynamical timescales. For small accretion rates, we find that the SL is unstable for heating instability that disrupts the initial latitudinal symmetry and produces large deviations between the two hemispheres. This instability also results in breaking of the axial symmetry as coherent flow structures are formed and escape from the SL intermittently. At enhanced accretion rates, the SL is prone to shearing instability and acts as a source of oblique waves that propagate towards the poles, leading to patterns that again break the axial symmetry. We compute artificial light curves of an SL viewed at different inclination angles. Most of the simulated light curves show oscillations at frequencies close to 1 kHz. We interpret these oscillations as inertial modes excited by shear instabilities near the boundary of the SL. Their frequencies, dependence on flux, and amplitude variations can explain the high-frequency pair quasi-periodic oscillations observed in many low-mass X-ray binaries.

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