Torque reversals and pulse profile of the pulsar 4U 1626-67

Abstract

We review the pulse profile evolution of the unique accretion powered X-ray pulsar 4U 1626-67 over the last 40 years since its discovery. This pulsar showed two distinct eras of steady spin-up separated by a steady spin-down episode for about 18 years. In the present work, using data from different observatories active during each phase of spin-up and spin-down we establish a clear correlation between the accretion torque acting on this pulsar and its pulse profile. The energy resolved pulse profiles are identical in both the spin-up eras and quite different in the spin-down era, especially in the low energy band. This correlation, along with the already known feature of strong Quasi Periodic Oscillations (QPO) that was present only in the spin-down era, clearly establish two different accretion modes onto the neutron star which produce different pulse profiles and only one of which produces the QPOs.

17 pages

References in corpus (19)

• The Swift X-ray Telescope
• Observations of Accreting Pulsars
• Calibration of the Rossi X-ray Timing Explorer Proportional Counter Array
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• High-Speed Optical Photometry of the Ultracompact X-ray Binary 4U 1626-67
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• Possible Detection of an Emission Cyclotron Resonance Scattering Feature from the Accretion-powered Pulsar 4U 1626-67
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• A study of the long term evolution of quasi periodic oscillations in the accretion powered X-ray pulsar 4U 1626-67
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Cited by in corpus (20)

• GRO J1744-28: an intermediate B-field pulsar in a low mass X-ray binary
• Spectral and Timing Analysis of the accretion-powered pulsar 4U 1626-67 observed with Suzaku and NuSTAR
• A broadband self-consistent modelling of the X-ray spectrum of 4U 1626--67
• Observations of 4U 1626-67 with the Imaging X-ray Polarimetry Explorer
• Luminosity dependent change of the emission diagram in the X-ray pulsar 4U 1626-67
• EXTraS discovery of an 1.2-s X-ray pulsar in M 31
• Pulse phase dependence of emission lines in the X-ray pulsar 4U 1626-67
• On the Torque Reversals of Accreting Neutron Stars
• On the torque reversals of 4U 1626--67
• Evolution of timing and spectral characteristics of 4U 1901+03 during its 2019 outburst using the Swift and NuSTAR observatories
• 4U 1626-67 Returns to Spin-Down: Timing features toe the line
• The X-ray Pulsar 2A 1822-371 as a Super Eddington source
• Properties and observability of glitches and anti-glitches in accreting pulsars
• Neutron Stars in X-ray Binaries and their Environments
• On the peculiar torque reversals and the X-ray luminosity history of the accretion-powered X-ray pulsar 4U 1626--67
• SALT observation of X-ray pulse reprocessing in 4U 1626-67
• Changes in the pulse phase dependence of X-ray emission lines in 4U 1626-67 with a torque reversal
• Sidebands to mHz QPOs in 4U 1626$-$67 in the second spin-down state
• Timing and Spectral Analysis of 4U 1626-67 Using AstroSat/LAXPC
• Probing accretion dynamics and spin evolution in the X-ray pulsar RX J0520.5-6932 during its 2024 Outburst