Discovery of kilohertz quasi-periodic oscillations and state transitions in the low-mass X-ray binary 1E~1724-3045 (Terzan 2)

Abstract

We have studied the rapid X-ray time variability in 99 pointed observations with the Rossi X-ray Timing Explorer (RXTE)'s Proportional Counter Array of the low-mass X-ray binary 1E~1724--3045 which includes, for the first time, observations of this source in its island and banana states, confirming the atoll nature of this source. We report the discovery of kilohertz quasi-periodic oscillations (kHz QPOs). Although we have 5 detections of the lower kHz QPO and one detection of the upper kHz QPO, in none of the observations we detect both QPOs simultaneously. By comparing the dependence of the rms amplitude with energy of kHz QPOs in different atoll sources, we conclude that this information cannot be use to unambiguously identify the kilohertz QPOs as was previously thought. We find that Terzan~2 in its different states shows timing behavior similar to that seen in other neutron-star low mass X-ray binaries (LMXBs). We studied the flux transitions observed between February 2004 and October 2005 and conclude that they are due to changes in the accretion rate.

arXiv comment16 pages, 13 figures, accepted for publication in ApJ

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• Phase-coherent timing of the accreting millisecond pulsar SAX J1748.9-2021
• The kilohertz quasi-periodic oscillations during the Z and atoll phases of the unique transient XTE J1701--462
• Deep Hubble Space Telescope Imaging of Globular Clusters Towards the Galactic Bulge: Observations, Data Reduction and Color-Magnitude Diagrams
• Spectral state evolution of 4U~1820-30: the stability of the spectral index of Comptonization tail
• The time derivative of the kilohertz quasi-periodic oscillations in 4U 1636-53
• Discovery of a correlation between the frequency of the mHz quasi-periodic oscillations and the neutron-star temperature in the low-mass X-ray binary 4U 1636-53
• High-frequency variability in neutron-star low-mass X-ray binaries
• On the geometric nature of low-frequency quasi-periodic oscillations in neutron-star low-mass X-ray binaries
• Discovery of a 7 mHz X-Ray Quasi-periodic Oscillation from the most Massive Stellar-mass Black Hole IC 10 X-1
• Broad iron emission line and kilohertz quasi-periodic oscillations in the neutron star system 4U 1636-53
• Probing spectral and temporal evolution of the neutron star low-mass X-ray binary 4U 1724-30 with AstroSat
• Kilohertz quasi-periodic oscillations in neutron-star X-ray binaries: Flattening of the lag spectrum with increasing luminosity
• The failed state transition of the ATOLL source GRS 1724-308