Quasi-periodic oscillations in the X-ray flux of Cyg X-2

Hasinger, G.; Langmeier, A.; Sztajno, M.; Trümper, J.; Lewin, W. H. G.; White, N. E.

doi:10.1038/319469a0

Cited by 42 publications

(17 citation statements)

References 16 publications

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“…Wijnands et al (1998) reported the simultaneous detection of twin kHz peaks at 500 and 860 Hz and highest single kHz QPO at 1007 Hz. The source exhibited 18 − 50 Hz QPOs in the HB and 5.6 Hz QPOs in the normal branch (Hasinger et al 1986;Elsner et al 1986;Wijnands et al 1997;Kuulkers et al 1999).…”

mentioning

confidence: 99%

NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus X-2

Mondal

Dewangan

Pahari

et al. 2017

Monthly Notices of the Royal Astronomical Society

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We report on the NuSTAR observation of the Z-type neutron star low-mass X-ray binary Cygnus X-2 performed on 7 January 2015. During this observation, the source exhibited a sudden decrease in count rate (dips) and stronger variability in 3 − 79 keV X-ray lightcurve. The hardness-intensity diagram shows that the source remained in the so-called "normal branch" of the Z-track, although an extended "flaring branch" is observed during the dips. The source was in a soft spectral state with the 3 − 45 keV luminosity of L ≃ (0.5 − 1.1) × 10 38 erg s −1 , assuming a distance of 8 kpc. Both the non-dip and dip X-ray spectra are well represented by models in which the soft band is dominated by the emission from the disc, while the hard X-ray band is dominated by the Comptonized emission from the boundary layer/corona and its reflected emission from the disc. The X-ray spectrum also revealed a broad Fe Kα emission line which is nearly symmetric at the higher flux and asymmetric when the flux is reduced by a factor of ∼ 2. The relativistic reflection model predicts the inner radius of the accretion disc as R in ≃ 2.5 − 6.0 R ISCO (≃ 30 − 73 Km) for the non-dip state and R in ≃ 2.0 − 2.6 R ISCO (≃ 24 − 32 Km) for the dip state. If the inner disc is truncated due to the pressure arising from a magnetic field, this implies an upper limit of the magnetic field strength of 7.6 × 10 9 G at the magnetic poles which is consistent with other estimates.

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mentioning

confidence: 99%

NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus X-2

Mondal

Dewangan

Pahari

et al. 2017

Monthly Notices of the Royal Astronomical Society

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“…A binary period of 9.8 days, other orbital parameters, and the mass limits of the two components of this binary system were measured by Cowley, Crampton, & Hutchings (1979). This is a low-mass X-ray binary and a typical Z source that shows type I X-ray bursts (Kahn & Grindlay 1984 ;Smale 1998), 18È50 Hz quasi-periodic oscillations (QPOs) in the horizontal branch, and 5.6 Hz QPOs in the nominal branch (Hasinger et al 1986 ;Elsner et al 1986 ;Wijnands et al 1997 ;Kuulkers, Wijnands, & van der Klis 1999). Recently, with RXT E, kilohertz QPOs with two peaks have also been detected from this source (Wijnands et al 1998).…”

Section: Introductionmentioning

confidence: 99%

Changes in the Long‐Term Intensity Variations in Cygnus X‐2 and LMC X‐3

Paul

Kitamoto

Makino

2000

ApJ

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We report the detection of changes in the long-term intensity variations in two X-ray binaries, Cyg X-2 and LMC X-3. In this work, we have used the long-term light curves obtained with the All-Sky Monitors (ASMs) of the Rossi X-Ray T iming Explorer (RXT E), Ginga, Ariel 5, and V ela 5B and the scanning modulation collimator of HEAO 1. It is found that in the light curves of both the sources, obtained with these instruments at various times over the last 30 years, more than one periodic or quasiperiodic component is always present. The multiple prominent peaks in the periodograms have frequencies unrelated to each other. In Cyg X-2, RXT E-ASM data show strong peaks at 40.4 and 68.8 days, and Ginga-ASM data show strong peaks at 53.7 and 61.3 days. Multiple peaks are also observed in LMC X-3. The various strong peaks in the periodograms of LMC X-3 appear at 104, 169, and 216 days (observed with RXT E-ASM) and 105, 214, and 328 days (observed with Ginga-ASM). The present results, when compared with the earlier observations of periodicities in these two systems, demonstrate the absence of any stable long period. The 78 day periodicity detected earlier in Cyg X-2 was probably due to the short time base in the RXT E data that were used, and the periodicity of 198 days in LMC X-3 was due to a relatively short duration of observation with HEAO 1.

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“…This is a typical LMXB Z-source containing a neutron star accreting at the Eddington limit (van der Klis 2004). Hasinger et al (1986) discovered a QPO at frequency 30 Hz increasing to 45 Hz with increasing source luminosity. HFQPOs (at ν l ∼ 700 Hz and ν u ∼ 1000 Hz) were then discovered by Wijnands et al (1998), while correlations between the QPO frequencies, the flux and the spectral index were established in Titarchuk et al (2007).…”

Section: Cygnus X-2mentioning

confidence: 96%

QPOs in the time domain: an autocorrelation analysis

Fukumura

Shrader

Dong

et al. 2010

A&A

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Context. Motivated by the recent proposal that one can obtain quasi-periodic oscillations (QPOs) by photon echoes manifesting as non-trivial features in the autocorrelation function (ACF), we study the ACFs of the light curves of three accreting black hole candidates and a neutron star already known to exhibit QPOs namely, GRS 1915+105, XTE J1550-564, XTE J1859+226 and Cygnus X-2. Aims. We present a comparative study of the timing properties of these systems in the frequency and time domain in search for similarities/differences that may provide clues to the physics underlying the QPO phenomenon. Methods. We compute and focus on the form of the ACFs in search of systematics or specific temporal properties at the time scales associated with the known QPO frequencies in comparison with the corresponding PDS. Results. Even within our small object sample we find both similarities as well as significant and subtle differences in the form of the ACFs both amongst black holes and between black holes and neutron stars to warrant a closer look at the QPO phenomenon in the time domain: the QPO features manifest as an oscillatory behavior of the ACF at lags near zero; the oscillation damps exponentially on time scales equal to the inverse QPO width to a level of a percent or so. In black holes this oscillatory behavior is preserved and easily discerned at much longer lags while this is not the case for the neutron star system Cyg X-2. The ACF of GRS 1915+105 provides an exception to this general behavior in that its decay is linear in time indicating an undamped oscillation of coherent phase. We present simple ad hoc models that reproduce these diverse time domain behaviors and we speculate that their origin is the phase coherence of the underlying oscillation.Conclusions. It appears plausible that time domain analyses, complementary to the more common frequency domain ones, could impose tighter constraints and provide clues for the driving mechanisms behind the QPO phenomenon.

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Quasi-periodic oscillations in the X-ray flux of Cyg X-2

Cited by 42 publications

References 16 publications

NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus X-2

NuSTAR view of the Z-type neutron star low-mass X-ray binary Cygnus X-2

Changes in the Long‐Term Intensity Variations in Cygnus X‐2 and LMC X‐3

QPOs in the time domain: an autocorrelation analysis

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