4U 1626-67 as seen by Suzaku before and after the 2008 torque reversal

Abstract

Aims. The accretion-powered pulsar 4U 1626-67 experienced a new torque reversal at the beginning of 2008, after about 18 years of steadily spinning down. The main goal of the present work is to study this recent torque reversal that occurred in 2008 February. Methods. We present a spectral analysis of this source using two pointed observations performed by Suzaku in 2006 March and in 2010 September. Results. We confirm with Suzaku the presence of a strong emission-line complex centered on 1 keV, with the strongest line being the hydrogen-like Ne Ly-alpha at 1.025(3) keV. We were able to resolve this complex with up to seven emission lines. A dramatic increase of the intensity of the Ne Ly-alpha line after the 2008 torque reversal occurred, with the equivalent width of this line reaching almost the same value measured by ASCA in 1993. We also report on the detection of a cyclotron line feature centered at ~37 keV. In spite of the fact that an increase of the X-ray luminosity (0.5-100 keV) of a factor of ~2.8 occurred between these two observations, no significant change in the energy of the cyclotron line feature was observed. However, the intensity of the ~1 keV line complex increased by an overall factor of ~8. Conclusions. Our results favor a scenario in which the neutron star in 4U 1626-67 accretes material from a geometrically thin disk during both the spin-up and spin-down phases.

7 pages, 5 figures and 2 tables. Accepted in A&A

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Cited by in corpus (23)

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• Application of the Ghosh & Lamb Relation to the Spin-up/down Behavior in the X-ray Binary Pulsar 4U 1626-67
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• Observations of 4U 1626-67 with the Imaging X-ray Polarimetry Explorer
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• 4U 1626-67 Returns to Spin-Down: Timing features toe the line
• Constraints on the disc-magnetosphere interaction in accreting pulsar 4U 1626--67
• On the peculiar torque reversals and the X-ray luminosity history of the accretion-powered X-ray pulsar 4U 1626--67
• Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal
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• Timing and Spectral Analysis of 4U 1626-67 Using AstroSat/LAXPC
• Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67