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Title: Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal.
Authors: Beri, Aru
Paul, Biswajit
Dewangan, Gulab C
Keywords: pulsars
Issue Date: Mar-2018
Publisher: Oxford University Press for The Royal Astronomical Society
Citation: Monthly Notices of the Royal Astronomical Society, 2018, Vol. 475, p999-1009
Abstract: We report results from an observation with the XMM–Newton observatory of a unique X-ray pulsar 4U 1626−67. European Photon Imaging Camera-pn data during the current spin-up phase of 4U 1626−67 have been used to study pulse phase dependence of low-energy emission lines. We found strong variability of low-energy emission line at 0.915 keV with the pulse phase, varying by a factor of 2, much stronger than the continuum variability. Another interesting observation is that behaviour of one of the low-energy emission lines across the pulse phase is quite different from that observed during the spin-down phase. This indicates that the structures in the accretion disc that produce pulse phase dependence of emission features have changed from spin-down to spin-up phase. This is well supported by the differences in the timing characteristics (like pulse profiles, quasi periodic oscillations, etc.) between spin-down and spin-up phases. We have also found that during the current spin-up phase of 4U 1626−67, the X-ray pulse profile below 2 keV is different compared to the spin-down phase. The X-ray light curve also shows flares which produce a feature around 3 mHz in power density spectrum of 4U 1626−67. Since flares are dominant at lower energies, the feature around 3 mHz is prominent at low energies.
Description: Open Access
ISSN: 0035-8711
1365-2966 - (online)
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Copyright: 2018 The authors & the Royal Astronomical Society.
Appears in Collections:Research Papers (A&A)

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