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Title: A study of the long-term evolution of quasi-periodic oscillations in the accretion-powered X-ray pulsar 4U 1626-67
Authors: Kaur, Ramanpreet
Paul, Biswajit
Kumar, Brijesh
Sagar, R.
Keywords: Binaries: Close
Pulsars: Individual: Alphanumeric: 4U 1626-67
Stars: Neutron, X-Rays: Binaries
Issue Date: Apr-2008
Publisher: University of Chicago Press for the American Astronomical Society
Citation: Astrophysical Journal, 2008, Vol.676, p1184-1188
Abstract: We report here a study of the long-term properties of quasiperiodic oscillations (QPOs) in an unusual accreting X-ray pulsar, 4U 1626-67. This is a unique accretion-powered X-ray pulsar in which we have found the QPOs to be present during all sufficiently long X-ray observations with a wide range of X-ray observatories. In the present spin-down era of this source, the QPO central frequency is found to be decreasing. In the earlier spin-up era of this source, there are only two reports of QPO detections, in 1983 with EXOSAT and 1988 with Ginga with an increasing trend. The QPO frequency evolution in 4U 1626-67 during the last 22 years changed from a positive to a negative trend, somewhat coincident with the torque reversal in this source. In the accretion-powered X-ray pulsars, the QPO frequency is directly related to the inner radius of the accretion disk, as per the Keplerian frequency model (KFM) and the beat frequency mdel (BFM). A gradual depletion of accretion disk is reported earlier from the X-ray spectral, flux, and pulse profile measurements. The present QPO frequency evolution study shows that X-ray flux and mass accretion rate may not change by the same factor; hence the simple KFM and BFM are not able to explain the QPO evolution in this source. This is the only X-ray pulsar to show persistent QPOs and is also the first accreting X-ray pulsar in which the QPO history is reported for a long timescale relating it with the long-term evolution of the accretion disk.
Description: Restricted Access. Articles older than 2 years are open to all at the journal site (alternative location)
ISSN: P-ISSN : 0004-637X.
E-ISSN : 1538-4357
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Copyright: 2008: The American Astronomical Society
Appears in Collections:Research Papers (A&A)

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