Discovery of a Second Kilohertz Quasi-periodic Oscillation Peak in 4U 1608-52. Méndez, M., van der Klis, M., van Paradijs, J., Lewin, W. H. G., Vaughan, B. A., Kuulkers, E., Zhang, W., Lamb, F. K., & Psaltis, D. The Astrophysical Journal, 494(1):L65, February, 1998. ![Discovery of a Second Kilohertz Quasi-periodic Oscillation Peak in 4U 1608-52 [link]](https://bibbase.org/img/filetypes/link.svg "link")
Paper doi abstract bibtex Using a new technique to improve the sensitivity to weak quasi-periodic oscillations (QPOs), we discovered a new QPO peak at about 1100 Hz in the March 1996 outburst observations of 4U 1608-52, simultaneous with the ~600-900 Hz peak previously reported from these data. The frequency separation between the upper and the lower QPO peaks varied significantly from 232.7+/-11.5 Hz on March 3 to 293.1+/-6.6 Hz on March 6. This is the first case of a variable kilohertz peak separation in an atoll source. We discuss to what extent this result could be accommodated in beat-frequency models such as proposed for the kilohertz QPOs. We measured the rms fractional amplitude of both QPOs as a function of energy, and we found that the relation is steeper for the lower than for the upper frequency peak. This is the first source where such a difference between the energy spectrum of the two kilohertz QPOs could be measured. \textlessP /\textgreater
@article{mendezDiscoverySecondKilohertz1998,
title = {Discovery of a {Second} {Kilohertz} {Quasi}-periodic {Oscillation} {Peak} in {4U} 1608-52},
volume = {494},
issn = {0004-637X},
url = {https://ui.adsabs.harvard.edu/abs/1998ApJ...494L..65M/abstract},
doi = {10.1086/311162},
abstract = {Using a new technique to improve the sensitivity to weak quasi-periodic oscillations (QPOs), we discovered a new QPO peak at about 1100 Hz in the March 1996 outburst observations of 4U 1608-52, simultaneous with the {\textasciitilde}600-900 Hz peak previously reported from these data. The frequency separation between the upper and the lower QPO peaks varied significantly from 232.7+/-11.5 Hz on March 3 to 293.1+/-6.6 Hz on March 6. This is the first case of a variable kilohertz peak separation in an atoll source. We discuss to what extent this result could be accommodated in beat-frequency models such as proposed for the kilohertz QPOs. We measured the rms fractional amplitude of both QPOs as a function of energy, and we found that the relation is steeper for the lower than for the upper frequency peak. This is the first source where such a difference between the energy spectrum of the two kilohertz QPOs could be measured. {\textless}P /{\textgreater}},
language = {en},
number = {1},
urldate = {2019-11-11},
journal = {The Astrophysical Journal},
author = {Méndez, M. and van der Klis, M. and van Paradijs, J. and Lewin, W. H. G. and Vaughan, B. A. and Kuulkers, E. and Zhang, W. and Lamb, F. K. and Psaltis, D.},
month = feb,
year = {1998},
pages = {L65},
}
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The frequency separation between the upper and the lower QPO peaks varied significantly from 232.7+/-11.5 Hz on March 3 to 293.1+/-6.6 Hz on March 6. This is the first case of a variable kilohertz peak separation in an atoll source. We discuss to what extent this result could be accommodated in beat-frequency models such as proposed for the kilohertz QPOs. We measured the rms fractional amplitude of both QPOs as a function of energy, and we found that the relation is steeper for the lower than for the upper frequency peak. 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