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Publication Details
AFRICAN RESEARCH NEXUS
SHINING A SPOTLIGHT ON AFRICAN RESEARCH
earth and planetary sciences
Discovery of twin kHz QPOs in the peculiar X-ray binary Circinus X-1
Astrophysical Journal, Volume 653, No. 2 I, Year 2006
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Description
We report the discovery with the RXTE PCA of twin kHz QPOs in the peculiar X-ray binary Circinus X-1. Eleven cases of simultaneous double QPOs occurred, with significances of up to 6.3 and 5.5 σ and centroid frequencies ranging between approximately 56 and 225 and 230 and 500 Hz for the two QPO peaks, respectively, i.e., for the most part at frequencies well below those of other sources. The QPO properties clearly indicate that these double peaks are the kHz QPOs known from low magnetic field neutron stars, and not black hole high-frequency QPOs, confirming that Cir X-1 is a neutron star, as suspected since the detection of type I X-ray bursts from the field of the source 20 years ago. The kHz QPO peak separation varies over a wide range, ∼175-340 Hz, and increases as a function of kHz QPO frequency. This is contrary to what has been observed in other sources but in good agreement with predictions of the relativistic precession model and Alfvén wave models; beat-frequency models require modification to accommodate this. In other observations, single kHz QPOs can be seen down to frequencies as low as ∼12 Hz, as well as a strong low-frequency quasi-periodic oscillation (LF QPO) between 1 and 30 Hz. The relations between the kHz QPOs and the LF QPO are in good agreement with those found previously in Z sources, confirming that Cir X-1 may be a peculiar Z source. We suggest that the low-frequency range over which the kHz QPOs occur in Cir X-1 and to a lesser extent in (other) Z sources, might be due to a stronger radial accretion flow relative to the disk flow than in other kHz QPO sources, possibly related to the nature of the companion star. © 2006. The American Astronomical Society. All rights reserved.
Authors & Co-Authors
van der Klis, Michiels D.
Netherlands, Amsterdam
Universiteit Van Amsterdam
Altamirano, Diego
Netherlands, Amsterdam
Universiteit Van Amsterdam
Klein-Wolt, Marc
Netherlands, Amsterdam
Universiteit Van Amsterdam
Wijnands, Rudy
Netherlands, Amsterdam
Universiteit Van Amsterdam
Jonker, Peter G.
Netherlands, Utrecht
Sron Netherlands Institute for Space Research
United States, Cambridge
Harvard-smithsonian Center for Astrophysics
Netherlands, Utrecht
Universiteit Utrecht
Fender, Robert P.
Netherlands, Amsterdam
Universiteit Van Amsterdam
United Kingdom, Southampton
University of Southampton
Statistics
Citations: 77
Authors: 6
Affiliations: 6
Identifiers
Doi:
10.1086/508934
ISSN:
0004637X