High-frequency quasi-periodic oscillations in black hole binaries (original) (raw)
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High-Frequency Quasi-periodic Oscillations in the Black Hole X-Ray Transient XTE J1650-500
Astrophysical Journal, 2003
We report the detection of high frequency variability in the black hole X-ray transient XTE J1650-500. A quasi-periodic oscillation (QPO) was found at 250 Hz during a transition from the hard to the soft state. We also detected less coherent variability around 50 Hz, that disappeared when the 250 Hz QPO showed up. There are indications that when the energy spectrum hardened the QPO frequency increased from ~110 Hz to ~270 Hz, although the observed frequencies are also consistent with being 1:2:3 harmonics of each other. Interpreting the 250 Hz as the orbital frequency at the innermost stable orbit around a Schwarzschild black hole leads to a mass estimate of 8.2 Msun. The spectral results by Miller et al.(2002, ApJ, 570, L69), which suggest considerable black hole spin, would imply a higher mass.
Studies of quasi-periodic oscillations in the black hole transient XTE J1817-330
Monthly Notices of the Royal Astronomical Society, 2010
We have used archival RXTE PCA data to investigate timing and spectral characteristics of the transient XTE J1817-330. The data pertains to 160 PCA pointed observations made during the outburst period 2006, January 27 to August 2. A detailed analysis of Quasi-Periodic Oscillations (QPOs) in this black hole X-ray binary is carried out. Power density spectra were obtained using the light curves of the source. QPOs have been detected in the 2-8 keV band in 10 of the observations. In 8 of these observations, QPOs are present in the 8-14 keV and in 5 observations in the 15-25 keV band. XTE J1817-330 is the third black hole source from which the low frequency QPOs are clearly detected in hard X-rays. The QPO frequency lies in ≈ 4-9 Hz and the rms amplitude in 1.7-13.3% range, the amplitude being higher at higher energies. We have fitted the PDS of the observations with Lorentzian and power law models. Energy spectra are derived for those observations in which the QPOs are detected to investigate any dependence of the QPO characteristic on the spectral parameters. These spectra are well fitted with a two component model that includes the disk black body component and a power law component. The QPO characteristics and their variations are discussed and its implication on the origin of the QPOs are examined.
High-frequency quasi-periodic oscillations from GRS 1915+105
Monthly Notices of the Royal Astronomical Society, 2013
We report the results of a systematic timing analysis of all archival Rossi X-Ray Timing Explorer (RXTE) observations of the bright black hole binary GRS 1915+105 in order to detect highfrequency quasi-periodic oscillations (HFQPOs). We produced power-density spectra in two energy bands and limited the analysis to the frequency range 30-1000 Hz. We found 51 peaks with a single-trial significance larger than 3σ. As all but three have centroid frequencies that are distributed between 63 and 71 Hz, we consider most of them significant regardless of the number of trials involved. The average centroid frequency and full width at half-maximum are 67.3 ± 2.0 Hz and 4.4 ± 2.4 Hz, respectively. Their fractional rms varies between 0.4 and 2 per cent (total band detections) and between 0.5 and 3 per cent (hard band detections). As GRS 1915+105 shows large variability on timescales longer than 1 s, we analysed the data in 16 s intervals and found that the detections are limited to a specific region in the colour-colour diagram, corresponding to state B of the source, when the energy spectrum is dominated by a bright accretion disc component. However, the rms spectrum of the HFQPO is very hard and does not show a flattening up to 40 keV, where the fractional rms reaches 11 per cent. We discuss our findings in terms of current proposed models and compare them with the results on other black hole binaries and neutron-star binaries.
A possible imprint of quasi-periodic oscillations in the X-ray spectra of black hole binaries
Astronomy & Astrophysics, 2016
Context. While nobody would deny the presence of quasi-periodic oscillations in the power density spectrum of black hole binaries nor their importance in the understanding of the mechanisms powering the X-ray emissions, the possible impact on the time-averaged disk energy spectrum from the phenomenon responsible for quasi-periodic oscillations is largely ignored in models of sources emission. Aims. Here we investigate the potential impact of such a structure on the resultant energy spectrum. Methods. Using data from the well-documented outbursts of XTE J1550-564, we looked at possible hints that the presence of quasiperiodic oscillations actually impacts the energy spectrum emitted by the source. In particular, we look at the evolution of the relation between the inner disk radius and the inner disk temperature obtained from fits to the spectral data. We then test this further by developing a simple model to simulate the spectrum of a disk with a structure mimicking quasi-periodic oscillations that are increasing in strength simulated results to those obtained from real data. Results. We detect a similar departure in the inner radius-inner temperature curve coming from the standard fit of our simulated observations as is seen in XTE J1550-564 data. We interpret our results as evidence that the structure at the origin of the quasi-periodic oscillations impacts the energy spectrum. Conclusions. Furthermore, in states with significant disk emission the inaccuracy of the determination of the disk parameters increases with the strength of quasi-periodic oscillations, an increase that then renders the value given by the fit unreliable for strong quasiperiodic oscillations.
Mechanisms for High‐Frequency Quasi‐periodic Oscillations in Neutron Star and Black Hole Binaries
The Astrophysical Journal, 1998
We explain the millisecond variability detected by Rossi X-ray Timing Explorer (RXTE) in the X-ray emission from a number of low mass X-ray binary systems (Sco X-1, 4U1728-34, 4U1608-522, 4U1636-536, 4U0614+091, 4U1735-44, 4U1820-30, GX5-1 and etc) in terms of dynamics of the centrifugal barrier, a hot boundary region surrounding a neutron star (NS). We demonstrate that this region may experience the relaxation oscillations, and that the displacements of a gas element both in radial and vertical directions occur at the same main frequency, of order of the local Keplerian frequency. We show the importance
The Astrophysical Journal, 1999
We study systematically the ≃ 0.1 − 1200 Hz quasi-periodic oscillations (QPOs) and broad noise components observed in the power spectra of non-pulsing neutron-star and black-hole low-mass X-ray binaries. We show that among these components we can identify two, occurring over a wide range of source types and luminosities, whose frequencies follow a tight correlation. The variability components involved in this correlation include neutron-star kilohertz QPOs and horizontal-branch oscillations, as well as black-hole QPOs and noise components. Our results suggest that the same types of variability may occur in both neutron-star and black-hole systems over three orders of magnitude in frequency and with coherences that vary widely but systematically. Confirmation of this hypothesis will strongly constrain theoretical models of these phenomena and provide additional clues to understanding their nature.
Astrophysical Journal, 1997
We have detected high-frequency (HF) quasi-periodic oscillations (QPOs) from the low-mass X-ray binary 4U 1820Ϫ303 during observations performed in 1996 October using the Rossi X-ray Timing Explorer. The QPOs are visible when the source occupies the low-state luminosity range L X ϭ 2.4 -3.1 ϫ 10 37 ergs s Ϫ1 (2-20 keV, at 6.4 kpc); the centroid frequency of the main QPO peak varies between 546 H 2 Hz and 796 H 6 Hz and is tightly correlated with the source count rate. The measured QPO widths are typically 120 Hz, with mean rms amplitude 4.1% H 0.3%. At the upper end of this luminosity range a second significant QPO peak appears with frequency 1065 H 7 Hz, width 40 H 20 Hz, and rms amplitude 3.2% H 0.8%. When both QPOs are visible simultaneously, the difference between their frequencies is 275 H 8 Hz. When the source brightens beyond L X ϭ 3.1 ϫ 10 37 ergs s Ϫ1 (110% of the Eddington limit for a helium-rich envelope), neither QPO is detected. Neither the magnetospheric beat frequency model nor the sonic point model of HF QPOs provides a perfect explanation of the phenomenology we observe.
Astrophysics and Space Science Proceedings, 2018
We discuss the spectral and timing analysis, and the mass determination of transient sources using a few phenomenological models other than TCAF solution (like photon index and QPO frequency correlation method). Then we discuss the relative feasibility of TCAF solution in determining the same quantities, and the additional information and insight that our method can provide. Taking forward from that, we will discuss how the spectral and timing properties of persistent sources generally agree with those of the transient sources under TCAF paradigm. Thus from the perspective of the accretion flow dynamics, there is really not much difference between these two types of objects. Finally, we will discuss how the variability of the class variable sources such as GRS 1915+105 can also be explained under the purview of TCAF solution and therefore this paradigm provides a common platform for the analysis of all such objects.
Timing Spectroscopy of Quasi-Periodic Oscillations in the Low-Mass X-Ray Neutron Star Binaries
The Astrophysical Journal, 1999
Precise simultaneous measurements of the frequencies of the two kiloHertz quasi-periodic oscillations (referred in the literature as upper and lower kHz QPOs) cast doubts on the validity of the simple beat-frequency interpretation and some of the modifications introduced to explain the results of the varying frequency difference. A new model explains the variation of the frequency difference suggesting that the upper kHz QPO, namely ν h is an upper hybrid frequency of the Keplerian oscillator under the influence of the Coriolis force and the lower kHz QPO is the Keplerian frequency ν K . Such an oscillator has two branches characterized by high frequency ν h (∼ 1 kHz) and by low frequency ν L (∼ 50 Hz). The frequency ν L depends strongly on the angle δ between the normal to the neutron star disk and Ω -the angular velocity of the magnetosphere surrounding the neutron star. In the lower part of the QPO spectrum (∼ 10 Hz), this model identifies the frequency of radial viscous oscillations ν v (previously called "extra noise component") and the break frequency ν b , which is associated with the diffusive process in the transition region (the innermost part of the disk). According to this model, all frequencies (namely ν h , ν L , ν b and ν v ) have specific dependences on ν K . This paper focuses on the verification of the predicted relations. For the source 4U 1728-34, the best theoretical fit is obtained for δ = 8.3 ± 1.0 o , which is slightly larger than δ = 5.5 ± 0.5 o previously found for Sco X-1. In addition, we show that the theoretically derived power law relation ν b ∝ ν 1.61 v is consistent with the recent observations of other atoll and Z-sources.
The Astrophysical Journal, 2000
We suggest that persistent low-frequency quasi-periodic oscillations (QPOs) detected in the black hole (BH) sources XTE J1118+480, GRO J1655-40 LMC X-1 at ∼ 0.1 Hz, and QPOs in HZ Her/Her X-1 at ∼ 0.05 Hz and in Neutron Star (NS) binaries 4U 1323-62, 4U 1746-31 and EXO 0748-76 at ∼ 1 Hz are caused by the global disk oscillations in the direction normal to the disk (normal mode). We argue that these disk oscillations are a result of the gravitational interaction between the central compact object and the disk. A small displacement of the disk from the equatorial plane results in a linear gravitational restoring force opposite to this displacement. Our analysis shows that the frequency of this mode is a function of the mass of the central object and it also depends on the inner and outer radii of the disk which in turn are related to the rotation period of the binary system. We derive an analytical formula for the frequency of the normal disk mode and show that these frequencies can be related to the persistent lower QPO frequencies observed in the NS and BH sources. We offer a new independent approach to the black hole mass determination by interpreting this low QPO frequency as the global disk oscillation frequency. The implementation of this method combined with the independent method which uses the X-ray energy spectra ) results in stringent constraints for the black hole masses.