Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52

M. Méndez, M. Van Der Klis, J. Van Paradijs, W. H G Lewin, B. A. Vaughan, E. Kuulkers, W. Zhang, F. K. Lamb, Dimitrios Psaltis

Research output: Contribution to journalArticle

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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 ∼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.

Original languageEnglish (US)
JournalAstrophysical Journal
Volume494
Issue number1 PART II
StatePublished - 1998
Externally publishedYes

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oscillation
oscillations
beat frequencies
atoll
outburst
energy
energy spectra
sensitivity

Keywords

  • Accretion, accretion disks
  • Stars: individual (4U 1608-52)
  • Stars: neutron
  • X-rays: stars

ASJC Scopus subject areas

  • Space and Planetary Science

Cite this

Méndez, M., Van Der Klis, M., Van Paradijs, J., Lewin, W. H. G., Vaughan, B. A., Kuulkers, E., ... Psaltis, D. (1998). Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52. Astrophysical Journal, 494(1 PART II).

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, Dimitrios.

In: Astrophysical Journal, Vol. 494, No. 1 PART II, 1998.

Research output: Contribution to journalArticle

Méndez, M, Van Der Klis, M, Van Paradijs, J, Lewin, WHG, Vaughan, BA, Kuulkers, E, Zhang, W, Lamb, FK & Psaltis, D 1998, 'Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52', Astrophysical Journal, vol. 494, no. 1 PART II.
Méndez M, Van Der Klis M, Van Paradijs J, Lewin WHG, Vaughan BA, Kuulkers E et al. Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52. Astrophysical Journal. 1998;494(1 PART II).
Méndez, M. ; Van Der Klis, M. ; Van Paradijs, J. ; Lewin, W. H G ; Vaughan, B. A. ; Kuulkers, E. ; Zhang, W. ; Lamb, F. K. ; Psaltis, Dimitrios. / Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52. In: Astrophysical Journal. 1998 ; Vol. 494, No. 1 PART II.
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AU - Van Der Klis, M.

AU - Van Paradijs, J.

AU - Lewin, W. H G

AU - Vaughan, B. A.

AU - Kuulkers, E.

AU - Zhang, W.

AU - Lamb, F. K.

AU - Psaltis, Dimitrios

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AB - 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.

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