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 Torque Reversals in Disk Accreting Pulsars

1998 ◽  
Vol 15 (2) ◽  
pp. 250-253
Author(s):  
Jianke Li ◽  
Dayal T. Wickramasinghe
Keyword(s):  
Neutron Star ◽  
Binary System ◽  
Recent Work ◽  
Time Scale ◽  
Accretion Rate ◽  
Future Studies ◽  
X Ray ◽  
The Past ◽  
X Ray Binaries ◽  
Coherent Picture

AbstractX-ray binaries in which the accreting component is a neutron star commonly exhibit significant changes in their spin. In the system Cen X-3, a disk accreting binary system, the pulsar was observed to spin up at a rate ḟ = 8 × 10−13 Hz s−1 when averaged over the past twenty years, but significant fluctuations were observed above this mean. Recent BASTE observations have disclosed that these fluctuations are much larger than previously noted, and appeared to be a system characteristic. The change in the spin state from spin-up to spin-down or vice-versa occurs on a time scale that is much shorter than the instrument can resolve (≤1 d), but appears always to be a similar amplitude, and to occur stochastically. These observations have posed a problem for the conventional torque–mass accretion relation for accreting pulsars, because in this model the spin rate is closely related to the accretion rate, and the latter needs to be finely tuned and to change abruptly to explain the observations. Here we review recent work in this direction and present a coherent picture that explains these observations. We also draw attention to some outstanding problems for future studies.

QUASI PERIODIC OSCILLATIONS IN X-RAY NEUTRON STAR AND PROBES OF PERIHELION PRECESSION OF GENERAL RELATIVITY

2002 ◽  
Vol 11 (04) ◽  
pp. 503-510 ◽  
Author(s):  
C. M. ZHANG
Keyword(s):  
Neutron Star ◽  
Accretion Rate ◽  
Second Harmonic ◽  
Harmonic Frequency ◽  
Periodic Oscillations ◽  
Perihelion Precession ◽  
X Ray ◽  
Outer Disk ◽  
Low Mass ◽  
X Ray Binaries

We ascribe the twin kilohertz Quasi Periodic Oscillations (kHz QPOs) of X-ray spectra of Low Mass X-Ray Binaries (LMXBs) to the pseudo-Newtonian Keplerian frequency and the apogee and perigee precession frequency of the same matter in the inner disk, and ascribe 15–60 Hz QPO (HBO) to the apogee (or perigee) precession and its second harmonic frequency to both apogee and perigee precession in the outer disk boundary of the neutron star (NS) magnetosphere. The radii of the inner and outer disks are correlated each other by a factor of two is assumed. The obtained conclusions include: all QPO frequencies increase and frequency difference of twin kHz QPOs decreases with increasing the accretion rate. The obtained theoretical relations between HBO frequency and twin kHz QPOs are simlilar to the measured empirical formula. Further, the theo-retical formula to calculate the NS mass by the twin kHz QPOs is proposed, and the resultant values are in the range of 1.4 to 1.8 M⊙. QPOs from LMXBs likely provide an accurate laboratory for a strong gravitational field, by which a new method to determine the NS masses of LMXBs is suggested.

scholarly journals A minimal timescale for the continuum in 4U 1608-52 and Aql X-1

2021 ◽  
Vol 502 (1) ◽  
pp. L72-L78
Author(s):  
K Mohamed ◽  
E Sonbas ◽  
K S Dhuga ◽  
E Göğüş ◽  
A Tuncer ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Power Spectra ◽  
Light Curves ◽  
State Transitions ◽  
Strong Positive Correlation ◽  
Present Evidence ◽  
X Ray ◽  
X Ray Binaries ◽  
The Continuum

ABSTRACT Similar to black hole X-ray binary transients, hysteresis-like state transitions are also seen in some neutron-star X-ray binaries. Using a method based on wavelets and light curves constructed from archival Rossi X-ray Timing Explorer observations, we extract a minimal timescale over the complete range of transitions for 4U 1608-52 during the 2002 and 2007 outbursts and the 1999 and 2000 outbursts for Aql X-1. We present evidence for a strong positive correlation between this minimal timescale and a similar timescale extracted from the corresponding power spectra of these sources.

scholarly journals The Beat-Frequency Interpretation of Kilohertz Quasi-periodic Oscillations in Neutron Star Low-Mass X-Ray Binaries

1998 ◽  
Vol 501 (1) ◽  
pp. L95-L99 ◽  
Author(s):  
Dimitrios Psaltis ◽  
Mariano Méndez ◽  
Rudy Wijnands ◽  
Jeroen Homan ◽  
Peter G. Jonker ◽  
...  
Keyword(s):  
Neutron Star ◽  
Beat Frequency ◽  
Periodic Oscillations ◽  
X Ray ◽  
Frequency Interpretation ◽  
Low Mass ◽  
X Ray Binaries

scholarly journals Statistical properties of twin kilohertz quasi-periodic oscillations in neutron star low-mass X-ray binaries

2014 ◽  
Vol 335 (2) ◽  
pp. 168-177 ◽  
Author(s):  
D. H. Wang ◽  
L. Chen ◽  
C. M. Zhang ◽  
Y. J. Lei ◽  
J. L. Qu
Keyword(s):  
Neutron Star ◽  
Statistical Properties ◽  
Periodic Oscillations ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

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).

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