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Discovery of kilohertz quasi-periodic oscillations and shifted frequency correlations in the accreting millisecond pulsar XTE J1807-294

Discovery of kilohertz quasi-periodic oscillations and shifted frequency correlations in the accreting millisecond pulsar XTE J1807-294
Discovery of kilohertz quasi-periodic oscillations and shifted frequency correlations in the accreting millisecond pulsar XTE J1807-294
We report the discovery of twin kilohertz quasi-periodic oscillations (kHz QPOs) in the X-ray flux of XTE J1807-294, the fourth accreting millisecond pulsar (AMP). This is the second AMP exhibiting twin kHz QPOs. In contrast to the first case, SAX J1808.4-3658, the frequency separation Δν between these kHz QPOs is consistent with the pulse frequency (190.6 Hz), not with half that value, confirming for the first time from pulsation measurements the inference, based on burst oscillations, that "slow rotators" (spin frequency less than 400 Hz) have Δν approximately equal to the spin frequency. While the QPOs move in frequency together over a range of more than 200 Hz, Δν remains constant with an average value of 205 ± 6 Hz. Variability components were found in the 5-130 Hz range, similar to those seen in other LMXBs. The correlations between the QPO and noise frequencies are also similar to those in other sources, but shifted by a factor of 1.59 in kHz QPO frequencies, similar to the factor of 1.45 shift found for SAX J1808.4-3658. Our results argue in favor of a spin-related formation mechanism for twin kHz QPOs and against a spin-related cause of the shift in the frequency correlations.
0004-637X
1250-1260
Linares, Manuel
d501c137-c3eb-45ca-b05c-4d4040b42b7b
van der Klis, Michiel
673255ce-dd17-4da0-910c-e3cb78460636
Altamirano, Diego
d5ccdb09-0b71-4303-9538-05b467be075b
Markwardt, Craig B.
c958d3b7-3e7a-4bdb-964d-3b1195438b4f
Linares, Manuel
d501c137-c3eb-45ca-b05c-4d4040b42b7b
van der Klis, Michiel
673255ce-dd17-4da0-910c-e3cb78460636
Altamirano, Diego
d5ccdb09-0b71-4303-9538-05b467be075b
Markwardt, Craig B.
c958d3b7-3e7a-4bdb-964d-3b1195438b4f

Linares, Manuel, van der Klis, Michiel, Altamirano, Diego and Markwardt, Craig B. (2005) Discovery of kilohertz quasi-periodic oscillations and shifted frequency correlations in the accreting millisecond pulsar XTE J1807-294. The Astrophysical Journal, 634 (2), 1250-1260. (doi:10.1086/497025).

Record type: Article

Abstract

We report the discovery of twin kilohertz quasi-periodic oscillations (kHz QPOs) in the X-ray flux of XTE J1807-294, the fourth accreting millisecond pulsar (AMP). This is the second AMP exhibiting twin kHz QPOs. In contrast to the first case, SAX J1808.4-3658, the frequency separation Δν between these kHz QPOs is consistent with the pulse frequency (190.6 Hz), not with half that value, confirming for the first time from pulsation measurements the inference, based on burst oscillations, that "slow rotators" (spin frequency less than 400 Hz) have Δν approximately equal to the spin frequency. While the QPOs move in frequency together over a range of more than 200 Hz, Δν remains constant with an average value of 205 ± 6 Hz. Variability components were found in the 5-130 Hz range, similar to those seen in other LMXBs. The correlations between the QPO and noise frequencies are also similar to those in other sources, but shifted by a factor of 1.59 in kHz QPO frequencies, similar to the factor of 1.45 shift found for SAX J1808.4-3658. Our results argue in favor of a spin-related formation mechanism for twin kHz QPOs and against a spin-related cause of the shift in the frequency correlations.

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Published date: 2005
Organisations: Astronomy Group

Identifiers

Local EPrints ID: 358796
URI: http://eprints.soton.ac.uk/id/eprint/358796
ISSN: 0004-637X
PURE UUID: 896e8046-04e3-4b1a-8964-21bb977b5b17
ORCID for Diego Altamirano: ORCID iD orcid.org/0000-0002-3422-0074

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Date deposited: 25 Oct 2013 08:28
Last modified: 10 Dec 2019 01:34

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Author: Manuel Linares
Author: Michiel van der Klis
Author: Craig B. Markwardt

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