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Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal

Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal
Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal

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 spinup 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 spindown 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.

67, Pulsars: individual: 4U 1626
0035-8711
999-1009
Beri, Aru
69ed346a-f02a-4243-83f9-ad5ab4c4008c
Paul, Biswajit
8f098150-c9db-4200-b3ea-cecdaa74cba6
Dewangan, Gulab C.
0062ef4f-8422-4085-a1de-8c72f472843c
Beri, Aru
69ed346a-f02a-4243-83f9-ad5ab4c4008c
Paul, Biswajit
8f098150-c9db-4200-b3ea-cecdaa74cba6
Dewangan, Gulab C.
0062ef4f-8422-4085-a1de-8c72f472843c

Beri, Aru, Paul, Biswajit and Dewangan, Gulab C. (2018) Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal. Monthly Notices of the Royal Astronomical Society, 475 (1), 999-1009. (doi:10.1093/mnras/stx3121).

Record type: Article

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 spinup 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 spindown 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.

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More information

Accepted/In Press date: 29 November 2017
e-pub ahead of print date: 29 November 2017
Published date: 21 March 2018
Keywords: 67, Pulsars: individual: 4U 1626

Identifiers

Local EPrints ID: 418305
URI: https://eprints.soton.ac.uk/id/eprint/418305
ISSN: 0035-8711
PURE UUID: edcca9f0-a1ea-44d2-a7c2-c652164096ef

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Date deposited: 27 Feb 2018 17:31
Last modified: 27 Feb 2018 17:31

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Contributors

Author: Aru Beri
Author: Biswajit Paul
Author: Gulab C. Dewangan

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