Discovery of KiloHertz Quasi-Periodic Oscillations in 4U 1735-44

Abstract

We discovered a single kHz quasi-periodic oscillation (QPO) near 1150 Hz in the Rossi X-ray Timing Explorer X-ray light curve of the low mass X-ray binary and atoll source 4U 1735-44. The rms amplitude of this peak was 2-3%, and the FWHM 6-40 Hz. There are indications that the kHz QPO frequency decreased from 1160 Hz to 1145 Hz when the count rate increased, which would be quite different from what is observed in other atoll sources for which kHz QPOs have been discovered. In the X-ray color-color diagram and hardness-intensity diagram the source traced out the curved branch (the so-called banana branch) which has been found by previous instruments. The kHz QPO was only detected when the source was at the lowest count rates during our observations, i.e. on the lower part of the banana branch. When 4U 1735-44 was at higher count rates, i.e. on the upper part of the banana branch and at higher inferred mass accretion rate with respect to that on the lower part of the banana branch, the QPO was not detected. Besides the kHz QPO we discovered a low frequency QPO with a frequency near 67 Hz, together with a complex broad peaked noise component below 30 Hz. This 67 Hz QPO may be related to the magnetospheric beat-frequency QPO, which is observed on the horizontal branch of Z sources. This idea is supported by the (peaked) noise found in both 4U 1735-44 and Z sources at frequencies just below the QPO frequency.

9 pages, including 2 figures. Accepted for publication in ApJ Letters

References in corpus (2)

• Lense-Thirring Precession and QPOs in Low Mass X-Ray Binaries
• Milli-second Oscillations in the Persistent and Bursting Flux of Aql X-1 During an Outburst

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• The atoll source states of 4U 1608-52
• Correlation Between Energy Spectral States and Fast Time Variability and Further Evidence for the Marginally Stable Orbit in 4U 1820-30
• Relations Between Timing Features and Colors in the X-Ray Binary 4U 0614+09
• The power spectral properties of the Z-source GX 340+0
• On the maximum amplitude and coherence of the kilohertz quasi-periodic oscillations in low-mass X-ray binaries
• A self-consistent approach to the hard and soft states of 4U 1705-44
• Discovery of a 57-69 Hz quasi-periodic oscillation in GX13+1
• Discovery of a Second Kilohertz QPO in the X-ray Binary 4U 1735-44
• Discovery of Kilohertz QPOs in the Atoll X-Ray Binary 4U 1705-44
• Discovery of a ~7 Hz Quasi-Periodic Oscillation in the low-luminosity low-mass X-ray binary 4U 1820-30
• The discovery of a 7-14 Hz Quasi-Periodic Oscillation in the X-ray Transient XTE J1806-246
• Disk Accretion onto Magnetized Neutron Stars: The Inner Disk Radius and Fastness Parameter
• Drop of coherence of the lower kilo-Hz QPO in neutron stars: is there a link with the innermost stable circular orbit?
• Investigation of the emission radii of kHz QPOs for the accreting millisecond X-Ray pulsars, Atoll and Z sources
• Stability of the photon indices in Z-source GX 340+0 for spectral states
• Discovery of twin kHz quasi-periodic oscillations in the high galactic la titude X-ray transient XTE J2123--058
• Quasi Periodic Oscillations in Low Mass X-Ray Binaries and Constraints on the Equation of State of Neutron Star Matter
• The complete Z-diagram of LMC X-2
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• Evolution of cross-correlation and time lag of 4U 1735-44 along the branches
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• Classification of Power Density Spectrum Features and Estimation of the Delta-Invariant Value for the Z Source GX 340+0
• Testing the transition layer model of quasi-periodic oscillations in neutron star X-ray binarie
• Low and High Frequency Quasi-Periodic Oscillations in 4U1915-05
• BeppoSAX and XMM-Newton spectral study of 4U 1735-44