A transient high-coherence oscillation in 4U 1820–30

Belloni, T.; Parolin, I.; Casella, P.

doi:10.1051/0004-6361:20040335

Cited by 11 publications

(10 citation statements)

References 17 publications

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“…In a few atoll sources, similar QPOs varying between 5 and 14 Hz with a relatively high coherence were reported Belloni et al 2004). These detections and a low mass accretion rate in atoll sources pose a distinct challenge to the models explaining the 6 Hz NBO in Z sources.…”

Section: Discussionmentioning

confidence: 69%

COUPLED HBO AND NBO VARIATIONS IN THE Z SOURCE GX 5-1: INNER ACCRETION DISK AS THE LOCATION OF QPOs

Sriram

Rao

Choi

2011

ApJ

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The simultaneous and coupled evolution of horizontal branch oscillation (HBO) and normal branch oscillation (NBO) in Z-type sources suggests that the production of HBO is connected to NBO and is caused by changes in the physical/radiative properties of the inner accretion disk, although there is a lack of substantial spectral evidence to support this. In this Letter, we present the results of an analysis of an RXTE observation of the Z source GX 5-1, where the 6 Hz NBO is simultaneously detected along with an HBO at 51 Hz. The variations in the intensity and the associated power density spectrum indicate that the HBO and NBO are strongly coupled, originating from the same location in the inner accretion disk. The absence of HBO and NBO in the lower energy bands, an increase in the rms amplitude with energy, and a smooth transition among them suggest that they are produced in the hot inner regions of the accretion disk. Based on a spectral analysis, we found a signature of changing or physically modified inner disk front during the coupled HBO and NBO evolution. We explore the various models to explain the observed phenomenon and propose that the NBO is affiliated to the oscillations in the thick/puffed-up inner region of the accretion disk.

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Section: Discussionmentioning

confidence: 69%

COUPLED HBO AND NBO VARIATIONS IN THE Z SOURCE GX 5-1: INNER ACCRETION DISK AS THE LOCATION OF QPOs

Sriram

Rao

Choi

2011

ApJ

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“…Z-sources vary on timescales of minutes to hours. This is a subject of many previous investigations of Sco X-1 (see, for example, van der Bradshaw et al, 2003;Barnard et al, 2003;Belloni et al, 2004). Here we concentrate on specific properties of Sco X-1 related to the hard X-ray emission.…”

Section: Spectral Analysismentioning

confidence: 88%

X-Ray Spectral and Timing Behavior of Scorpius X-1. Spectral Hardening During the Flaring Branch

Titarchuk

Seifina²,

Shrader

2014

ApJ

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We present an analysis of the spectral and timing properties of X-ray emission from the Z-source Sco X-1 during its evolution between the Horizontal (HB) and Flaring (FB) branches observed with the Rossi X-ray Timing Explorer during the 1996 -2002 period. We find that the broad-band (3 -250 keV) energy spectra during all spectral states can be adequately reproduced by a model, consisting of two Comptonized components and an iron-line. We suggest that the seed photons of kT s1 < ∼ 0.7 keV coming from the disk and of temperature kT s2 < ∼ 1.8 keV coming from the neutron star (NS) are each upscattered by hot electrons of a "Compton cloud" (herein Comptb1 and Comptb2 components respectively with which are associated similarly subscripted parameters). The photon power-law index Γ 2 is almost constant (Γ 2 ∼ 2) for all spectral states. In turn, Γ 1 demonstrates a twophase behavior with the spectral state: Γ 1 is quasi-constant at the level Γ 1 ∼ 2 for the HB−NB and Γ 1 is less than 2, namely in the range of 1.3 < Γ 1 < 2, when source traces the FB. We also detect a decrease kT s2 from 1.8 keV to 0.7 keV during the FB. We interpret this apparent quasi-stability of the indices during the HB−NB in the framework of the model in which the spectrum is determined by the Comptonized thermal components. This established for the Comptonized spectral components of the Z-source Sco X-1 is similar to that was previously -2found in the atoll sources 4U 1728-34, GX 3+1 and 4U 1820-30 and the Z-source GX 340+0 through all spectral states. However we interpret the index reduction phase detected during the FB in Sco X-1 within the framework of a model in which the spectrum at the FB is determined by high radiation pressure from the NS surface.

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“…Their centroid frequencies are typically ∼ 1 − 70 Hz for NS-LMXBs, while ∼ 0.01 − 30 Hz for BH-LMXBs. In LMXBs, the timing behavior has been shown to be strongly connected to the spectral properties (Hasinger & van der Klis 1989;van der Klis 2006;van der Klis 1995;Homan et al 2001;Belloni et al 2004;Belloni et al 2005).…”

Section: Introductionmentioning

confidence: 99%

Correlations in Horizontal Branch Oscillations and Break Components in Xte J1701-462 and Gx 17+2

Chen

et al. 2015

ApJ

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We studied the horizontal branch oscillations (HBO) and the band-limited components observed in the power spectra of the transient neutron star low-mass X-ray binary XTE J1701-462 and the persistent "Sco-like" Z source GX 17+2.These two components were studied based on the state-resolved spectra. We found that the frequencies of XTE J1701-462 lie on the known correlations (WK and PBK), showing consistency with other types of X-ray binaries (black holes, atoll sources and millisecond X-ray pulsars). However, GX 17+2 is shifted from the WK correlation like other typical Z sources. We suggest that the WK/PBK main track forms a boundary which separates persistent sources from transient sources. The characteristic frequencies of break and HBO are independent of accretion rate in both sources, although it depends on spectral models. We also report the energy dependence of the HBO and break frequencies in XTE J1701-462 and how the temporal properties change with spectral state in XTE J1701-462 and GX 17+2. We studied the correlation between rms at the break and the HBO frequency. We suggest that HBO and break components for both sources probably arise from a similar physical mechanism: Comptonization emission from the corona. These two components could be caused by same kind of oscillation in a corona who with uneven density, and they could be generated from different areas of corona. We further suggest that different proportions of the Comptonization component in the total flux cause the different distribution between GX 17+2 and XTE J1701-462 in the rms break -rms HBO diagram. 1989; van der Klis 2006; van der Klis 1995; Homan et al. 2001; Belloni et al. 2004; Homan & Belloni 2005; Belloni et al. 2005). Based on X-ray spectra properties and rapid variability behaviors, bright NS-LMXBs are commonly classified into two sub-types, the Z sources and the atoll sources (Hasinger & van der Klis 1989). The Z sources have luminosity approaching the Eddington limit (∼ 0.1 − 1L Edd or more), while the atoll sources show luminosity of ∼ 0.01 − 0.5L Edd . The Color-Diagram (CD) and Hardness Intensity Diagram (HID) of a typical Z source include three branches, the horizontal branch (HB), the normal branch (NB), and the flare branch (FB). Depending on further details about the shape and orientation of these branches, the Z sources were further classified into the "Cyg-like" Z sources and the "Sco-like" Z sources. Three distinct types of LFQPOs were observed in the Fourier power density spectra of Z sources: horizontal branch oscillation (HBO) with centroid frequency ∼ 9.5 − 60 Hz, normal branch oscillation (NBO) with centriod frequency ∼ 6 − 20 Hz, and flare branch oscillation (FBO) with centroid frequency ∼ 20 Hz. Atoll sources also show ∼ 20 − 60 Hz LFQPOs.

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A transient high-coherence oscillation in 4U 1820–30

Cited by 11 publications

References 17 publications

COUPLED HBO AND NBO VARIATIONS IN THE Z SOURCE GX 5-1: INNER ACCRETION DISK AS THE LOCATION OF QPOs

COUPLED HBO AND NBO VARIATIONS IN THE Z SOURCE GX 5-1: INNER ACCRETION DISK AS THE LOCATION OF QPOs

X-Ray Spectral and Timing Behavior of Scorpius X-1. Spectral Hardening During the Flaring Branch

Correlations in Horizontal Branch Oscillations and Break Components in Xte J1701-462 and Gx 17+2

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