Pulse phase dependence of emission lines in the X-ray pulsar 4U 1626-67

Abstract

We present results from a pulse phase resolved spectroscopy of the complex emission lines around 1 keV in the unique accretion powered X-ray pulsar 4U 1626-67 using observation made with the XMM-Newton in 2003. In this source, the red and blue shifted emission lines and the line widths measured earlier with Chandra suggest their accretion disk origin. Another possible signature of lines produced in accretion disk can be a modulation of the line strength with pulse phase. We found the line fluxes to have pulse phase dependence, making 4U 1626-67 only the second pulsar after Her X-1 to show such variability. The O~VII line at 0.568~keV from 4U 1626-67 varied by a factor of $\sim$4, stronger than the continuum variability, that support their accretion disk origin. The line flux variability may appear due to variable illumination of the accretion disk by the pulsar or more likely, a warp like structure in the accretion disk. We also discuss some further possible diagnostics of the accretion disk in 4U 1626-67 with pulse phase resolved emission line spectroscopy.

Accepted for a publication in MNRAS

References in corpus (2)

• VLT spectroscopy and non-LTE modeling of the C/O-dominated accretion disks in two ultracompact X-ray binaries
• Torque reversals and pulse profile of the pulsar 4U 1626-67

Cited by in corpus (13)

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• Observations of 4U 1626-67 with the Imaging X-ray Polarimetry Explorer
• On the torque reversals of 4U 1626--67
• 4U 1626-67 Returns to Spin-Down: Timing features toe the line
• A Suzaku View of Accretion Powered X-ray Pulsar GX 1+4
• Neutron Stars in X-ray Binaries and their Environments
• 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
• The ongoing spin-down episode of 4U 1626-67
• Spectral analysis of ultraluminous X-ray pulsars with models of X-ray pulsars
• The Intensity Modulation of Fluorescent Line by a Finite Light Speed Effect in Accretion-Powered X-ray Pulsars
• Probing accretion dynamics and spin evolution in the X-ray pulsar RX J0520.5-6932 during its 2024 Outburst
• Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67