Discovery of Submillisecond Quasi-periodic Oscillations in the X-Ray Flux of Scorpius X-1

Klis, M.B.M. van der; Swank, J. H.; Zhang, W.; Jahoda, K.; Morgan, E.; Lewin, W. H. G.; Vaughan, Brian; Paradijs, J. van

doi:10.1086/310251

Cited by 222 publications

(150 citation statements)

References 16 publications

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“…Soon after the launch of the Rossi X-Ray Timing Explorer (RXTE), rapid (300-1300 Hz), nearly periodic variability in the X-ray light curves of low-mass X-ray binary (LMXB) systems was discovered (Strohmayer et al 1996;van der Klis et al 1996). These oscillations, referred to as kilohertz quasi-periodic oscillations (QPOs), have now been observed in over two dozen neutron star-bearing LMXBs (see van der Klis 2000 for a review).…”

Section: Introductionmentioning

confidence: 99%

A Compton Upscattering Model for Soft Lags in the Lower Kilohertz Quasi-periodic Oscillation in 4U 1608−52

Lee

Misra

Taam

2001

The Astrophysical Journal

108

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An empirical Compton upscattering model is described that reproduces both the fractional amplitude (rms) versus energy and the soft time lags in the ≈830 Hz quasi-periodic oscillation (QPO) observed in 4U 1608Ϫ52 on 1996 March 3. A combination of two coherent variations in the coronal and soft photon temperatures (with their relative contributions determined by enforcing energy conservation) gives rise to the QPO's energy-dependent characteristics. All input parameters to the model, save a characteristic plasma size and the fraction of Comptonized photons impinging on the soft photon source, are derived from the time-averaged photon energy spectrum of the same observation. Fits to the fractional rms and phase lag data for this kilohertz QPO imply that the spatial extent of the plasma is in the range from ∼4 to 15 km.

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Section: Introductionmentioning

confidence: 99%

A Compton Upscattering Model for Soft Lags in the Lower Kilohertz Quasi-periodic Oscillation in 4U 1608−52

Lee

Misra

Taam

2001

The Astrophysical Journal

108

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“…In all the Z sources, except GX 349+2 [9], we discovered kHz QPOs with frequencies between 300 and 1100 Hz on the horizontal branch [3][4][5][6][7][8]. Typical power density spectra of GX 5−1 and GX 340+0 showing the kHz QPOs in these sources are shown in Figure 2.…”

Section: Resultsmentioning

confidence: 99%

“…Typical power density spectra of GX 5−1 and GX 340+0 showing the kHz QPOs in these sources are shown in Figure 2. Figures of the kHz QPOs in the other sources can be found elsewhere (Scorpius X-1: [3,4]; GX 17+2: [5]; Cygnus X-2: [6]). The only source for which the kHz QPOs are also observed on the (lower) normal branch and the flaring branch is Scorpius X-1 [3,4].…”

Section: Resultsmentioning

confidence: 99%

KiloHertz quasi-periodic oscillations in the Z sources GX 340+0, Cygnus X-2, GX 17+2, GX 5–1, and Scorpius X-1

Wijnands

Klis

1998

AIP Conference Proceedings

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Abstract.We have discovered kiloHertz quasi-periodic oscillations (kHz QPOs) in five Z sources: GX 340+0, Cygnus X-2, GX 17+2, GX 5−1, and Scorpius X-1. In all sources the properties of these kHz QPOs are very similar and closely related to the position of the sources on the Z track traced out in the X-ray color-color diagram and the hardness-intensity diagram. The frequencies of the kHz QPOs increase when the sources move from the left end of the horizontal branch to horizontal/normal branch vertex, thus with inferred mass accretion rate. Only for Scorpius X-1 the kHz QPOs have been observed down the normal branch unto the flaring branch. The strength and the FWHM of the higherfrequency kHz QPOs decrease with mass accretion rate, but when the lowerfrequency kHz QPOs are detected the strength and the FWHM of this QPO stay approximately constant with mass accretion rate. In Scorpius X-1 the frequency separation between the kHz QPOs decreases with mass accretion rate, but in the other Z sources the separation remains approximately constant, although a similar decrease in peak separation as found in Scorpius X-1 can not be excluded.

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“…Depending on the quality factor Q = ν/∆ν, features are classified as broadband noise (Q 2), quasi-periodic oscillations (QPO, Q 2), coherent pulsations (∆ν smaller than the frequency bin). Many weakly-magnetized accreting neutron stars show a particular kind of QPOs, whose frequencies range from 300 to 1300 Hz, called for this reason kHz QPOs [2]. Very often kHz QPOs appear in pairs, with the two peaks, labelled "upper" and "lower", at frequencies differing by about 300 Hz.…”

Section: The Khz Qpo Phenomenonmentioning

confidence: 99%

The moving hotspot model for kHz QPOs in accreting neutron stars

Bachetti¹,

Romanova²,

Göǧüş³

et al. 2011

AIP Conference Proceedings

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Abstract. 3D MHD simulation of accretion onto neutron stars have shown in the last few years that the footprint (hotspot) of the accretion flow changes with time. Two different kinds of accretion, namely the funnel flow and the equatorial accretion produced by instabilities at the inner disk, produce different kinds of motion of the hotspot. The funnel flow produces hotspots that move around the magnetic pole, while instabilities produce other hotspots that appear randomly and move along the equator or slightly above. The angular velocities of the two hotspots are different, the equatorial one being higher and both close to the Keplerian velocity in the inner region. Modeling of the lightcurves of these hotspots with Monte Carlo simulations show that the signatures produced in power specra by them, if observed, are QPOs plus low frequency components. Their frequencies, general behavior and features describe correctly most of the properties of kHz QPOs, if we assume the funnel flow hotspots as the origin of the lower kHz QPO and instabilities as the origin of the upper kHz QPO. THE KHZ QPO PHENOMENONThe lightcurves of X-ray binaries often show a number of variability phenomena, that populate the power spectra of their lightcurves with different kinds of noise and oscillatory components. They are normally fitted with Lorentzian curves [1] and classified in terms of their characteristic frequency ν and their width ∆ν. Depending on the quality factor Q = ν/∆ν, features are classified as broadband noise (Q 2), quasi-periodic oscillations (QPO, Q 2), coherent pulsations (∆ν smaller than the frequency bin). Many weakly-magnetized accreting neutron stars show a particular kind of QPOs, whose frequencies range from 300 to 1300 Hz, called for this reason kHz QPOs [2]. Very often kHz QPOs appear in pairs, with the two peaks, labelled "upper" and "lower", at frequencies differing by about 300 Hz. Lower and upper peak generally differ for their properties, the lower peak being normally more coherent and appearing in a shorter frequency range [3,4]. Their frequencies are correlated with the ones of lower-frequency phenomena. KHz QPOs tend to have higher frequencies at higher countrates, but the correlation is not straightforward. On small timescales, in fact, the variation of the frequency with the countrate is usually very rapid, with the frequency going up of hundreds of Hz with slight increases of the countrate. If one plots the frequency of the oscillations versus the countrate, it is evident that the variation happens on different tracks, almost parallel to each other but distinct. Instead, there is a good correlation between the frequency and the spectral state [5], and at the lower and upper limits of their range the frequency difarXiv:1011.0142v1 [astro-ph.HE]

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Discovery of Submillisecond Quasi-periodic Oscillations in the X-Ray Flux of Scorpius X-1

Cited by 222 publications

References 16 publications

A Compton Upscattering Model for Soft Lags in the Lower Kilohertz Quasi-periodic Oscillation in 4U 1608−52

A Compton Upscattering Model for Soft Lags in the Lower Kilohertz Quasi-periodic Oscillation in 4U 1608−52

KiloHertz quasi-periodic oscillations in the Z sources GX 340+0, Cygnus X-2, GX 17+2, GX 5–1, and Scorpius X-1

The moving hotspot model for kHz QPOs in accreting neutron stars

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