Evidence of a decrease of kHz QPO peak separation towards low frequencies in 4U 1728-34 (GX 354-0)

Abstract

We have produced the colour-colour diagram of all the observations of 4U 1728-34 available in the Rossi X-ray Timing Explorer public archive (from 1996 to 2002) and found observations filling in a previously reported 'gap' between the island and the banana X-ray states. We have made timing analysis of these gap observations and found, in one observation, two simultaneous kHz quasi-periodic oscillations (QPOs). The timing parameters of these kHz QPOs fit in the overall trend of the source. The 'lower' kHz QPO has a centroid frequency of ~308 Hz. This is the lowest 'lower' kHz QPO frequency ever observed in 4U 1728-34. The peak frequency separation between the 'upper' and the 'lower' kHz QPO is 274+/-11 Hz, significantly smaller than the constant value of ~350 Hz found when the 'lower' kHz QPO frequency is between ~500 and 800 Hz. This is the first indication in this source for a significant decrease of kHz QPO peak separation towards low frequencies. We briefly compare the result to theoretical models for kHz QPO production.

accepted for publication in MNRAS Letters

References in corpus (17)

• Lense-Thirring Precession and QPOs in Low Mass X-Ray Binaries
• Millisecond Oscillations in X-Ray Binaries
• 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
• kHz Quasi Periodic Oscillations in Low Mass X-ray Binaries as Probes of General Relativity in the Strong Field Regime
• Nuclear-Powered Millisecond Pulsars and the Maximum Spin Frequency of Neutron Stars
• Quasi-periodic X-ray brightness fluctuations in an accreting millisecond pulsar
• A multi-Lorentzian timing study of the atoll sources 4U 0614+09 and 4U 1728-34
• RXTE observations of the neutron star low-mass X-ray binary GX 17+2: correlated X-ray spectral and timing behavior
• Precise Measurements of the Kilohertz Quasi-Periodic Oscillations in 4U 1728-34
• 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
• Study of the Temporal Behavior of 4U 1728-34 as a Function of its Position in the Color-Color Diagram
• Changing Frequency Separation of Kilohertz Quasi-Periodic Oscillations in the Sonic-Point Beat-Frequency Model
• Discovery of Two Simultaneous Kilohertz Quasi-Periodic Oscillations in KS 1731-260
• Timing Spectroscopy of Quasi-Periodic Oscillations in the Low-Mass X-ray Neutron Star Binaries
• KiloHertz quasi-periodic oscillations difference frequency exceeds inferred spin frequency in 4U 1636-53

Cited by in corpus (26)

• Detecting gravitational wave emission from the known accreting neutron stars
• The distribution of kHz QPO frequencies in bright LMXBs
• Modelling the spin equilibrium of neutron stars in LMXBs without gravitational radiation
• Relations Between Timing Features and Colors in Accreting Millisecond Pulsars
• Analysing the atolls: X-ray spectral transitions of accreting neutron stars
• Discovery of twin kHz QPOs in the peculiar X-ray binary Circinus X-1
• Is there a link between the neutron-star spin and the frequency of the kilohertz quasi-periodic oscillations?
• The correlations between the twin kHz QPO frequencies of LMXBs
• The X-ray spectrum of the bursting atoll source 4U~1728-34 observed with INTEGRAL
• Simultaneous radio and X-ray observations of the low-mass X-ray binary GX 13+1
• The correlations between the spin frequencies and kHz QPOs of Neutron Stars in LMXBs
• On the Constancy of the Photon Index of X-ray spectra of 4U~1728-34 through all spectral states
• AstroSat/LAXPC detection of milli-second phenomena in 4U 1728-34
• Investigation of the emission radii of kHz QPOs for the accreting millisecond X-Ray pulsars, Atoll and Z sources
• Reversal of the amplitude difference of kHz QPOs in six atoll sources
• Study of the X-ray properties of the neutron-star binary 4U 1728$-$34 from the soft to hard state
• Statistical properties of twin kHz QPO in neutron star LMXBs
• The Magneto Hydro Dynamical Model of KHz Quasi Periodic Oscillations in Neutron Star Low Mass X-ray Binaries (II)
• Possible twin kHz Quasi Periodic Oscillations in the accreting millisecond X-ray Pulsar IGR J17511-3057
• Correlations between the frequencies of twin kHz QPOs and spins of neutron stars in LMXBs
• The kHz QPOs as a probe of the X-ray color-color diagram and accretion-disk structure for the atoll source 4U 1728-34
• Probing the accretion disc structure by the twin kHz QPOs and spins of neutron stars in LMXBs
• How To Distinguish Neutron Star and Black Hole X-ray Binaries? Spectral index and Quasi-Periodic Oscillation Frequency Correlation
• Study on Correlations between the Twin Kilohertz Quasi-periodic Oscillations in Low-mass X-ray Binaries
• Application of the relativistic precession model to the accreting millisecond X-ray pulsar IGR J17511-3057
• QPOML: A Machine Learning Approach to Detect and Characterize Quasi-Periodic Oscillations in X-ray Binaries