Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/3917
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dc.contributor.authorJain, Chetana-
dc.contributor.authorPaul, Biswajit-
dc.contributor.authorDutta, Anjan-
dc.date.accessioned2010-07-22T04:55:29Z-
dc.date.available2010-07-22T04:55:29Z-
dc.date.issued2010-04-
dc.identifier.citationMonthly Notices of the Royal Astronomical Society, 2010, Vol.403, p920en
dc.identifier.issn1365-2966 -(Online)-
dc.identifier.issn0035-8711-
dc.identifier.urihttp://hdl.handle.net/2289/3917-
dc.descriptionRestricted Access. An open-access version is available at arXiv.org (one of the alternative locations)en
dc.description.abstract4U 1626− 67 is an accretion powered X-ray pulsar that shows remarkably stable X-ray luminosity above a time-scale of hours and gradual intensity variation on a time-scale of a few years. Unlike the other high magnetic field binary X-ray pulsars, the spin-up or spin-down rate of the neutron star is also very stable on time-scales up to several years. Here, we report a significant increase in the X-ray intensity in the long-term Rossi X-ray Timing Explorer (RXTE) All Sky Monitor light curve of 4U 1626− 67. Similar enhancement in the X-ray flux has also been detected in the Swift Burst Alert Telescope light curve. The increase in the X-ray flux took place over a long period of about 100 d and there appear to be two episodes of flux enhancement. We have investigated the spectral and timing features of 4U 1626− 67 during its current state of enhanced flux emission with data obtained from the Proportional Counter Array and the High-Energy X-ray Timing Explorer on board RXTE. We report the detection of a torque reversal to spin-up in 4U 1626− 67. The source has entered a new spin-up phase with a spin-up rate of 4.02(5) × 10−13 Hz s−1 . The present spin-up rate is almost half of the earlier spin-up and spin-down trends. A significant excess in soft X-ray photon emission is observed during the enhanced flux state, which is similar to the energy spectrum obtained during the spin-up era of the pulsar before 1990. 4U 1626− 67 is a unique accretion powered X-ray pulsar in which quasi-periodic oscillations have been consistently observed over the past ∼20 years. During the recent observations, however, we did not detect a quasi-periodic oscillation at frequencies as seen in earlier observations. Instead, we report detection of a significant broadening in the wings of the 130 mHz peak and a change in the shape of the continuum of the power spectrum. These results indicate that the flux enhancement is not a simple case of increased mass accretion rate, but there is also a change in the accretion geometry in the vicinity of the neutron star.en
dc.language.isoenen
dc.publisherWiley Interscience for the RASen
dc.relation.urihttp://adsabs.harvard.edu/abs/2010MNRAS.403..920Jen
dc.relation.urihttp://arxiv.org/abs/0906.4169en
dc.relation.urihttp://dx.doi.org/10.1111/j.1365-2966.2009.16170.xen
dc.rights2010 The Royal Astronomical Societyen
dc.subjectPulsarsen
dc.subjectX-ray binariesen
dc.subjectX-ray pulsaren
dc.subjectX-ray:starsen
dc.titleSpectral and temporal changes associated with flux enhancement in 4U 1626-67en
dc.typeArticleen
Appears in Collections:Research Papers (A&A)

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