CONSTRAINTS OF NEUTRON STAR MASS BY THE kHz QPO FREQUENCY

2011 ◽  
Vol 20 (10) ◽  
pp. 2033-2037
Author(s):  
C. M. ZHANG ◽  
Y. Y. PAN ◽  
Y. H. ZHAO ◽  
Y. CAI ◽  
J. WANG ◽  
...  
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Emission Spectra ◽  
Periodic Oscillations ◽  
X Ray ◽  
Star Mass ◽  
Neutron Star Mass ◽  
The Masses ◽  
Central Stars ◽  
The Way

Twin kHz quasi-periodic oscillations (QPOs) have been found in the emission spectra of about thirty X-ray neuron star systems, where the upper ones of twin QPOs are often interpreted as the Keplerian frequencies of the accreting matter orbiting around the central stars. The observations of the kHz QPOs can be used to constrain the masses of neutron stars (NSs), and in particular to imply the properties of the matters at nuclear densities. By the way, we discuss the preferences of some kHz QPO models that constrain the NS parameters.

scholarly journals A Bayesian approach to matching thermonuclear X-ray burst observations with models

2019 ◽  
Vol 490 (2) ◽  
pp. 2228-2240 ◽  
Author(s):  
A J Goodwin ◽  
D K Galloway ◽  
A Heger ◽  
A Cumming ◽  
Z Johnston
Keyword(s):  
Neutron Star ◽  
Rotation Axis ◽  
Line Of Sight ◽  
Type I ◽  
X Ray ◽  
Star Mass ◽  
Disc Model ◽  
Neutron Star Mass ◽  
Hydrogen Mass ◽  
Neutron Star Radius

ABSTRACT We present a new method of matching observations of Type-I (thermonuclear) X-ray bursts with models, comparing the predictions of a semi-analytic ignition model with X-ray observations of the accretion-powered millisecond pulsar SAX J1808.4–3658 in outburst. We used a Bayesian analysis approach to marginalize over the parameters of interest and determine parameters such as fuel composition, distance/anisotropy factors, neutron star mass, and neutron star radius. Our study includes a treatment of the system inclination effects, inferring that the rotation axis of the system is inclined $\left(69^{+4}_{-2}\right)^\circ$ from the observers line of sight, assuming a flat disc model. This method can be applied to any accreting source that exhibits Type-I X-ray bursts. We find a hydrogen mass fraction of $0.57^{+0.13}_{-0.14}$ and CNO metallicity of $0.013^{+0.006}_{-0.004}$ for the accreted fuel is required by the model to match the observed burst energies, for a distance to the source of $3.3^{+0.3}_{-0.2}\, \mathrm{kpc}$. We infer a neutron star mass of $1.5^{+0.6}_{-0.3}\, \mathrm{M}_{\odot }$ and radius of $11.8^{+1.3}_{-0.9}\, \mathrm{km}$ for a surface gravity of $1.9^{+0.7}_{-0.4}\times 10^{14}\, \mathrm{cm}\, \mathrm{s}^{-2}$ for SAX J1808.4–3658.

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 Burst-induced coronal cooling in GS 1826–24

2020 ◽  
Vol 634 ◽  
pp. A58 ◽  
Author(s):  
C. Sánchez-Fernández ◽  
J. J. E. Kajava ◽  
J. Poutanen ◽  
E. Kuulkers ◽  
V. F. Suleimanov
Keyword(s):  
Neutron Star ◽  
Emission Spectra ◽  
Spectral Shape ◽  
Type I ◽  
Simultaneous Observation ◽  
X Ray ◽  
Neutron Star Mass ◽  
Hard State ◽  
First Time ◽  
Burst Emission

Type I X-ray bursts in GS 1826–24, and in several other systems, may induce cooling of the hot inner accretion flow that surrounds the bursting neutron star. Given that GS 1826–24 remained persistently in the hard state over the period 2003–2008 and presented regular bursting properties, we stacked the spectra of the X-ray bursts detected by INTEGRAL (JEM-X and ISGRI) and XMM-Newton (RGS) during that period to study the effect of the burst photons on the properties of the Comptonizing medium. The extended energy range provided by these instruments allows the simultaneous observation of the burst and persistent emission spectra. We detect an overall change in the shape of the persistent emission spectrum in response to the burst photon shower. For the first time, we observe simultaneously a drop in the hard X-ray emission, together with a soft X-ray excess with respect to the burst blackbody emission. The hard X-ray drop can be explained by burst-induced coronal cooling, while the bulk of the soft X-ray excess can be described by fitting the burst emission with an atmosphere model, instead of a simple blackbody model. Traditionally, the persistent emission was assumed to be invariant during X-ray bursts, and more recently to change only in normalization but not in spectral shape; the observed change in the persistent emission level during X-ray bursts may thus trigger the revision of existing neutron star mass-radius constraints, as the derived values rely on the assumption that the persistent emission does not change during X-ray bursts. The traditional burst fitting technique leads to up to a 10% overestimation of the bolometric burst flux in GS 1826–24, which significantly hampers the comparisons of the KEPLER and MESA model against this “textbook burster”.

scholarly journals The effect of accretion on the measurement of neutron star mass and radius in the low-mass X-ray binary 4U 1608−52

2014 ◽  
Vol 442 (4) ◽  
pp. 3777-3790 ◽  
Author(s):  
Juri Poutanen ◽  
Joonas Nättilä ◽  
Jari J. E. Kajava ◽  
Outi-Marja Latvala ◽  
Duncan K. Galloway ◽  
...  
Keyword(s):  
Neutron Star ◽  
X Ray ◽  
Star Mass ◽  
Neutron Star Mass ◽  
Low Mass

scholarly journals CONSTRAINTS ON NEUTRON STAR MASS AND RADIUS IN GS 1826–24 FROM SUB-EDDINGTON X-RAY BURSTS

2012 ◽  
Vol 749 (1) ◽  
pp. 69 ◽  
Author(s):  
Michael Zamfir ◽  
Andrew Cumming ◽  
Duncan K. Galloway
Keyword(s):  
Neutron Star ◽  
X Ray ◽  
Star Mass ◽  
Neutron Star Mass

scholarly journals Multi-epoch X-ray burst modelling: MCMC with large grids of 1D simulations

2020 ◽  
Vol 494 (3) ◽  
pp. 4576-4589 ◽  
Author(s):  
Zac Johnston ◽  
Alexander Heger ◽  
Duncan K Galloway
Keyword(s):  
Neutron Star ◽  
Computational Models ◽  
Type I ◽  
Heating Rates ◽  
X Ray ◽  
Star Mass ◽  
Multiple Parameters ◽  
Parameter Estimations ◽  
Neutron Star Mass ◽  
System Properties

ABSTRACT Type-I X-ray bursts are recurring thermonuclear explosions on the surface of accreting neutron stars. Matching observed bursts to computational models can help to constrain system properties, such as the neutron star mass and radius, crustal heating rates, and the accreted fuel composition, but systematic parameter studies to date have been limited. We apply Markov chain Monte Carlo methods to 1D burst models for the first time, and obtain system parameter estimations for the ‘Clocked Burster’, GS 1826−238, by fitting multiple observed epochs simultaneously. We explore multiple parameters which are often held constant, including the neutron star mass, crustal heating rate, and hydrogen composition. To improve the computational efficiency, we precompute a grid of 3840 kepler models – the largest set of 1D burst simulations to date – and by interpolating over the model grid, we can rapidly sample burst predictions. We obtain estimates for a CNO metallicity of $Z_\mathrm{CNO} = 0.010^{+0.005}_{-0.004}$, a hydrogen fraction of $X_0 = 0.74^{+0.02}_{-0.03}$, a distance of $d \sqrt{\xi _\mathrm{b}} = 6.5^{+0.4}_{-0.6}\, \mathrm{kpc}$ , and a system inclination of $i = {69^{+2}_{-3}}^{\circ }$.

scholarly journals REFINED NEUTRON STAR MASS DETERMINATIONS FOR SIX ECLIPSING X-RAY PULSAR BINARIES

2011 ◽  
Vol 730 (1) ◽  
pp. 25 ◽  
Author(s):  
Meredith L. Rawls ◽  
Jerome A. Orosz ◽  
Jeffrey E. McClintock ◽  
Manuel A. P. Torres ◽  
Charles D. Bailyn ◽  
...  
Keyword(s):  
Neutron Star ◽  
X Ray ◽  
Star Mass ◽  
Neutron Star Mass
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