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; D. Psaltis

doi:10.1086/311162

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, D. Psaltis

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92 Scopus citations

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 language	English (US)
Pages (from-to)	L65-L69
Journal	Astrophysical Journal
Volume	494
Issue number	1 PART II
DOIs	https://doi.org/10.1086/311162
State	Published - 1998

Keywords

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

ASJC Scopus subject areas

Astronomy and Astrophysics
Space and Planetary Science

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10.1086/311162

Cite this

@article{293a0026222b4633a14fea0ab601596b,

title = "Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52",

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.",

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

author = "M. M{\'e}ndez and {Van Der Klis}, M. and {Van Paradijs}, J. and Lewin, {W. H.G.} and Vaughan, {B. A.} and E. Kuulkers and W. Zhang and Lamb, {F. K.} and D. Psaltis",

note = "Funding Information: This work was supported in part by the Netherlands Organization for Scientific Research (NWO) under grant PGS 78-277 and by the Netherlands Foundation for research in astronomy (ASTRON) under grant 781-76-017. M. M. is a fellow of the Consejo Nacional de Investigaciones Cient{\'i}ficas y T{\'e}c-nicas de la Rep{\'u}blica Argentina. W. H. G. L. acknowledges support from the National Aeronautics and Space Administration. J. V. P. acknowledges support from the National Aeronautics and Space Administration through contract NAG5-3269. F. K. L. acknowledges support from NSF, through grant AST 93-15133, and NASA, through grant 5-2925.",

year = "1998",

doi = "10.1086/311162",

language = "English (US)",

volume = "494",

pages = "L65--L69",

journal = "Astrophysical Journal",

issn = "0004-637X",

publisher = "IOP Publishing Ltd.",

number = "1 PART II",

}

TY - JOUR

T1 - Discovery of a second kilohertz quasi-periodic oscillation peak in 4U 1608-52

AU - Méndez, M.

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, D.

N1 - Funding Information: This work was supported in part by the Netherlands Organization for Scientific Research (NWO) under grant PGS 78-277 and by the Netherlands Foundation for research in astronomy (ASTRON) under grant 781-76-017. M. M. is a fellow of the Consejo Nacional de Investigaciones Científicas y Téc-nicas de la República Argentina. W. H. G. L. acknowledges support from the National Aeronautics and Space Administration. J. V. P. acknowledges support from the National Aeronautics and Space Administration through contract NAG5-3269. F. K. L. acknowledges support from NSF, through grant AST 93-15133, and NASA, through grant 5-2925.

PY - 1998

Y1 - 1998

N2 - 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.

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.

KW - Accretion, accretion disks

KW - Stars: individual (4U 1608-52)

KW - Stars: neutron

KW - X-rays: stars

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DO - 10.1086/311162

M3 - Article

AN - SCOPUS:0002926822

VL - 494

SP - L65-L69

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1 PART II

ER -

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

Abstract

Keywords

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