scholarly journals TESTING THE TWIN kHz QPO MODELS OF NEUTRON STAR

2013 ◽  
Vol 23 ◽  
pp. 144-147
Author(s):  
DE-HUA WANG ◽  
LI CHEN ◽  
JING WANG
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Power Law ◽  
The Other ◽  
Chi Square ◽  
Periodic Oscillations ◽  
Best Fitting ◽  
Z Sources ◽  
Twin Peak ◽  
Better Than

We take the data of twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron stars (NSs) published before 2011 as the samples, which include 15 Atoll sources and 8 Z sources. Then we test the correlation between the twin peak kHz QPOs, and compare with the samples. We find the power law relation between the lower-frequency (ν1) and the upper-frequency (ν2) of kHz QPOs can fit the data much better than the other models. For the Atoll (Z) sources, the best fitting coefficient and index of power law are a = 687 (720) and b =1.50 (1.83) respectively. The Chi-square per degree of freedom (χ2/d.o.f.) are 1.93 and 1.49 respectively.

STATISTICS OF TWIN kHz QPOs IN NEUTRON STARS

2013 ◽  
Vol 23 ◽  
pp. 148-151
Author(s):  
JING WANG ◽  
DE-HUA WANG ◽  
LI CHEN
Keyword(s):  
Neutron Stars ◽  
Quality Factor ◽  
Linear Model ◽  
Power Law ◽  
Peak Frequency ◽  
Published Data ◽  
Periodic Oscillations ◽  
Exponential Models ◽  
Z Sources ◽  
Better Than

We collect the recently published data of twin kilohertz quasi-periodic oscillations (kHz QPOs) in neutron stars (NSs), and analyze two kinds of samples for five Atoll sources and five Z sources. We study the the relation between the quality factor and the peak frequency of upper frequency. We take three possible models, i.e. linear, power-law and exponential models to fit the data and find that the power-law and the exponential models can reflect the relation better than the linear model.

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 Level of Satisfaction in the Use of the Wraparound Hawley and Thermoplastic Maxillary Retainers

2019 ◽  
Vol 90 (1) ◽  
pp. 63-68 ◽  
Author(s):  
Adenilson Silva Chagas ◽  
Karina Maria Salvatore Freitas ◽  
Rodrigo Hermont Cançado ◽  
Fabricio Pinelli Valarelli ◽  
Luiz Filiphe Gonçalves Canuto ◽  
...  
Keyword(s):  
The Other ◽  
Chi Square ◽  
Level Of Satisfaction ◽  
Intergroup Comparison ◽  
Significant Difference ◽  
Chi Square Test ◽  
Orthodontic Patients ◽  
Better Than

ABSTRACT Objective To compare the level of satisfaction in the use of wraparound Hawley and thermoplastic maxillary retainers. Materials and Methods The study sample included 70 orthodontic patients (24 males and 46 females), who were in the retention stage (mean age = 20.80 years). All patients wore the two types of maxillary retainer for 1 month each, along with a 3×3 fixed mandibular retainer. After the use of each retainer, the patients responded to a questionnaire evaluating the level of satisfaction with their use of the maxillary retainer. Intergroup comparison was performed by independent t tests. Chi-square test was used to evaluate preference for the type of retainer by gender. Results The thermoplastic retainer was better for swallowing and the wraparound Hawley appliance was better for hygiene and durability. The other factors evaluated (adaptation, speech, comfort, esthetics, satisfaction, and fitting) did not show significant differences between the retainers. There was also no significant difference in preference for the appliances. Conclusions Regarding the overall satisfaction and the preference, there was no difference between the wraparound Hawley and thermoplastic retainers. The wraparound Hawley appliance was better in hygiene and resistance than the thermoplastic retainer; and the thermoplastic appliance was better than the wraparound Hawley for swallowing fluids and saliva.

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 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 Models of high-frequency quasi-periodic oscillations and black hole spin estimates in Galactic microquasars

2020 ◽  
Vol 643 ◽  
pp. A31
Author(s):  
A. Kotrlová ◽  
E. Šrámková ◽  
G. Török ◽  
K. Goluchová ◽  
J. Horák ◽  
...  
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
High Frequency ◽  
Accretion Disc ◽  
The Other ◽  
Periodic Oscillations ◽  
X Ray ◽  
Upper Limit ◽  
Oscillation Modes

We explore the influence of nongeodesic pressure forces present in an accretion disc on the frequencies of its axisymmetric and nonaxisymmetric epicyclic oscillation modes. We discuss its implications for models of high-frequency quasi-periodic oscillations (QPOs), which have been observed in the X-ray flux of accreting black holes (BHs) in the three Galactic microquasars, GRS 1915+105, GRO J1655−40, and XTE J1550−564. We focus on previously considered QPO models that deal with low-azimuthal-number epicyclic modes, |m| ≤ 2, and outline the consequences for the estimations of BH spin, a ∈ [0, 1]. For four out of six examined models, we find only small, rather insignificant changes compared to the geodesic case. For the other two models, on the other hand, there is a significant increase of the estimated upper limit on the spin. Regarding the falsifiability of the QPO models, we find that one particular model from the examined set is incompatible with the data. If the spectral spin estimates for the microquasars that point to a >  0.65 were fully confirmed, two more QPO models would be ruled out. Moreover, if two very different values of the spin, such as a ≈ 0.65 in GRO J1655−40 and a ≈ 1 in GRS 1915+105, were confirmed, all the models except one would remain unsupported by our results. Finally, we discuss the implications for a model that was recently proposed in the context of neutron star (NS) QPOs as a disc-oscillation-based modification of the relativistic precession model. This model provides overall better fits of the NS data and predicts more realistic values of the NS mass compared to the relativistic precession model. We conclude that it also implies a significantly higher upper limit on the microquasar’s BH spin (a ∼ 0.75 vs. a ∼ 0.55).

scholarly journals Middle aged γ-ray pulsar J1957+5033 in X-rays: pulsations, thermal emission and nebula

2020 ◽  
Author(s):  
D A Zyuzin ◽  
A V Karpova ◽  
Y A Shibanov ◽  
A Y Potekhin ◽  
V F Suleimanov
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Power Law ◽  
Thermal Emission ◽  
Single Pulse ◽  
X Rays ◽  
Middle Aged ◽  
X Ray ◽  
Photon Index ◽  
Γ Ray

Abstract We analyze new XMM-Newton and archival Chandra observations of the middle-aged γ-ray radio-quiet pulsar J1957+5033. We detect, for the first time, X-ray pulsations with the pulsar spin period of the point-like source coinciding by position with the pulsar. This confirms the pulsar nature of the source. In the 0.15–0.5 keV band, there is a single pulse per period and the pulsed fraction is ≈18 ± 6 per cent. In this band, the pulsar spectrum is dominated by a thermal emission component that likely comes from the entire surface of the neutron star, while at higher energies (≳ 0.7 keV) it is described by a power law with the photon index Γ ≈ 1.6. We construct new hydrogen atmosphere models for neutron stars with dipole magnetic fields and non-uniform surface temperature distributions with relatively low effective temperatures. We use them in the spectral analysis and derive the pulsar average effective temperature of ≈(2 − 3) × 105 K. This makes J1957+5033 the coldest among all known thermally emitting neutron stars with ages below 1 Myr. Using the interstellar extinction–distance relation, we constrain the distance to the pulsar in the range of 0.1–1 kpc. We compare the obtained X-ray thermal luminosity with those for other neutron stars and various neutron star cooling models and set some constraints on latter. We observe a faint trail-like feature, elongated ∼8 arcmin from J1957+5033. Its spectrum can be described by a power law with a photon index Γ = 1.9 ± 0.5 suggesting that it is likely a pulsar wind nebula powered by J1957+5033.

scholarly journals Probing the X-ray Variability of X-ray Binaries

2003 ◽  
Vol 214 ◽  
pp. 236-239
Author(s):  
Wenfei Yu
Keyword(s):  
Neutron Star ◽  
Light Curve ◽  
Time Scale ◽  
Accretion Rate ◽  
Power Spectra ◽  
The Other ◽  
Periodic Oscillations ◽  
X Ray ◽  
Orbital Frequency ◽  
X Ray Binaries

Kilohertz quasi-periodic oscillations (kHz QPOs) has been regarded as representing the Keplerian frequency at the inner disk edge in the neutron star X-ray binaries. The so-called “parallel tracks” on the plot of the kHz QPO frequency vs. X-ray flux in neutron star X-ray binaries, on the other hand, show the correlation between the kHz QPO frequency and the X-ray flux on time scales from hours to days. This is suspected as caused by the variations of the mass accretion rate through the accretion disk surrounding the neutron star. We show here that by comparing the correlation between the kHz QPO frequency and the X-ray count rate on a certain QPO time scale observed approximately simultaneous in the Fourier power spectra of the X-ray light curve, we have found evidences that the X-ray flux of millihertz QPOs in neutron star X-ray binaries is generated inside the inner disk edge if adopting that the kilohertz QPO frequency is an orbital frequency at the inner disk edge.

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.

kHz QPO OBSERVATIONS AND PULSAR PARAMETERS

2012 ◽  
Vol 12 ◽  
pp. 414-418 ◽  
Author(s):  
C. M. ZHANG ◽  
Y. Y. PAN ◽  
J. WANG ◽  
A. TAANI ◽  
Y. H. ZHAO
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
Binary Systems ◽  
Periodic Oscillations ◽  
Strong Gravity

Neutron star parameters, e.g. mass, radius and magnetic field, can be constrained by the observations of kHz quasi-periodic oscillations (QPOs), which show the information close to the surface of neutron stars (NSs) in the accreting binary systems. The high QPO frequency will leak out the physics around the inner disk boundary, where the physics in a strong gravity regime will effect. By means of the twin kHz QPO detections, which are interpreted as the Keplerian orbital motions near NSs, the methods of determining NS mass and radius are introduced.

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