Kilohertz quasi-periodic oscillations in neutron-star X-ray binaries: Flattening of the lag spectrum with increasing luminosity

Abstract

We study the energy-dependent time lags and rms fractional amplitude of the kilohertz quasi-periodic oscillations (kHz QPOs) of a group of neutron-star low mass X-ray binaries (LMXBs). We find that for the lower kHz QPO the slope of the best-fitting linear model to the time-lag spectrum and the total rms amplitude integrated over the 2 to 25 keV energy band both decrease exponentially with the luminosity of the source. For the upper kHz QPO the slope of the time-lag spectrum is consistent with zero, while the total rms amplitude decreases exponentially with the luminosity of the source. We show that both the slope of the time-lag spectrum and the total rms amplitude of the lower kHz QPO are linearly correlated with a slope of ~1. Finally, we discuss the mechanism that could be responsible for the radiative properties of the kHz QPOs, with the variability originating in a Comptonising cloud or corona that is coupled to the innermost regions of the accretion disc, close to the neutron star.

arXiv comment7 pages, 5 figures, accepted for publication in MNRAS

References in corpus (55)

• Lense-Thirring Precession and QPOs in Low Mass X-Ray Binaries
• Thermonuclear (type-I) X-ray bursts observed by the Rossi X-ray Timing Explorer
• A Unified Description of the Timing Features of Accreting X-ray Binaries
• Sonic-Point Model of Kilohertz Quasi-Periodic Brightness Oscillations in Low-Mass X-ray Binaries
• X-ray reverberation around accreting black holes
• Photospheric radius expansion X-ray bursts as standard candles
• Probes and Tests of Strong-Field Gravity with Observations in the Electromagnetic Spectrum
• Discovery of Sub-Millisecond Quasi-Periodic Oscillations in the X-Ray Flux of Scorpius X-1
• Are There Three Peaks in the Power Spectra of GX 339-4 and Cyg X-1?
• Long Term Variability of Cyg X-1 I. X-ray spectral-temporal correlations in the hard state
• Boundary layer, accretion disk and X-ray variability in luminous LMXBs
• Spectral States of XTE J1701-462: Link between Z and Atoll Sources
• A multi-Lorentzian timing study of the atoll sources 4U 0614+09 and 4U 1728-34
• XTE J1701-462 and its Implications for the Nature of Subclasses in Low-Magnetic-Field Neutron Star Low-Mass X-Ray Binaries
• An abrupt drop in the coherence of the lower kilohertz QPO in 4U 1636-536
• Relations Between Timing Features and Colors in the X-Ray Binary 4U 0614+09
• RXTE observations of the first transient Z source XTE J1701-462: shedding new light on mass accretion in luminous neutron star LMXBs
• Discovery of a second kHz QPO peak in 4U 1608-52
• The coherence of kHz quasi-periodic oscillations in the X-rays from accreting neutron stars
• Kilohertz QPOs in Neutron Star Binaries modeled as Keplerian Oscillations in a Rotating Frame of Reference
• The Amplitude of the Kilohertz Quasi-periodic Oscillations in 4U 1728-34, 4U 1608-52, and Aql X-1, as a Function of X-ray Intensity
• The Comptonising medium of the neutron star in 4U 1636-53 through its lower kilohertz Quasi-Periodic Oscillations
• Study of the Temporal Behavior of 4U 1728-34 as a Function of its Position in the Color-Color Diagram
• What ignites on the neutron star of 4U 0614+091?
• Simultaneous Measurements of X-Ray Luminosity and Kilohertz Quasi-Periodic Oscillations in Low-Mass X-Ray Binaries
• On the maximum amplitude and coherence of the kilohertz quasi-periodic oscillations in low-mass X-ray binaries
• On the Correlated Spectral and Timing Properties of 4U 1636-53: an Atoll Source at High Accretion Rates
• Comptonization and QPO Origins in Accreting Neutron Star Systems
• Distances to Galactic X-ray Binaries with Gaia DR2
• Effects of Rapid Stellar Rotation on Equation of State Constraints Derived from Quasi-Periodic Brightness Oscillations
• A Compton Up-scattering Model for Soft Lags in the Lower Kilohertz QPO in 4U1608-52
• Energy Dependent Time Delays of kHz Oscillations due to Thermal Comptonization
• Supporting evidence for the signature of the innermost stable circular orbit in Rossi X-ray data from 4U1636-536
• The kilohertz quasi-periodic oscillations during the Z and atoll phases of the unique transient XTE J1701--462
• The cooling phase of Type-I X-ray bursts in 4U 1636-53
• Soft lags in neutron star kHz Quasi Periodic Oscillations: evidence for reverberation?
• Discovery of Microsecond Soft Lags in the X-Ray Emission of the Atoll Source 4U1636-536
• Discovery of microsecond time lags in kilohertz QPO
• Time lags of the kilohertz quasi-periodic oscillations in the low-mass X-ray binaries 4U 1608--52 and 4U 1636--53
• Measurement of Hard Lags and Coherences in the X-Ray Flux of Accreting Neutron Stars and Comparison with Accreting Black Holes
• Discovery of the upper kilo-Hz QPO from the X-ray transient Aql X-1
• Drop of coherence of the lower kilo-Hz QPO in neutron stars: is there a link with the innermost stable circular orbit?
• Rayleigh - Taylor Gravity Waves and Quasiperiodic Oscillation Phenomenon in X-ray Binaries
• The spectral-timing properties of upper and lower kHz QPOs
• A Systematic Spectral-Timing Analysis of Kilohertz Quasi-Periodic Oscillations in the Rossi X-ray Timing Explorer Archive
• Constraining the size of the Comptonizing medium by modeling the energy dependent time-lags of kHz QPOs of Neutron star system
• Discovery of kilohertz quasi-periodic oscillations and state transitions in the low-mass X-ray binary 1E~1724-3045 (Terzan 2)
• The cooling phase of Type I X-ray bursts observed with RXTE in 4U 1820-30 does not follow the canonical F - T^4 relation
• High-frequency variability in neutron-star low-mass X-ray binaries
• Relation between spectral changes and the presence of the lower kHz QPO in the neutron-star low-mass X-ray binary 4U 1636-53
• Relation between the properties of the kilohertz quasi-periodic oscillations and spectral parameters in 4U 1636$-$53
• Are the kHz QPO lags in neutron star 4U 1608-52 due to reverberation?
• Phase lags of quasi-periodic oscillations across source states in the low-mass X-ray binary 4U 1636-53
• The amplitude of the kilohertz quasi-periodic oscillations in 4U 1636$-$53 in the frequency-energy space
• Modeling the upper kHz QPOs of 4U 1728-34 with X-ray reverberation

Cited by in corpus (2)

• Spectro-temporal evolution of 4U 1702-429 using AstroSat-NICER
• Lags of the KiloHertz Quasi-Periodic Oscillations in the transient source XTE J1701$-$462