A broadband self-consistent modelling of the X-ray spectrum of 4U 1626--67

Abstract

The accretion-powered X-ray pulsar 4U 1626--67 is one of the few highly magnetized pulsars that accretes through Roche-lobe overflow from a low-mass companion. The characteristics of its broadband spectrum are similar to those of X-ray pulsars hosted in a high-mass X-ray binary systems, with a broad resonant cyclotron scattering feature (CRSF) at $\sim$37 keV. In this work, we examine the pulse-resolved and the pulse-averaged broadband spectrum using data from NuSTAR and Swift. We use the Becker & Wolff model of bulk+thermal Comptonization to infer key physical parameters of the accretion column flow and a broadband model for the disk reflected spectrum. In the softer X-ray band, we need to add a soft black-body component with $k{T}_{\mathrm{bb}}$ $\sim$0.5 keV, whose characteristics indicate a possible origin from the neutron star surface. Residuals suggest that the shape of the cyclotron line could be more satisfactorily fitted using a narrow core and broader wings and, at higher energies, a second harmonic could be present at $\sim$61 keV.

arXiv comment13 pages, accepted for publication in MNRAS

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Cited by in corpus (15)

• Cyclotron lines in highly magnetized neutron stars
• Decade long RXTE monitoring observations of Be/X-ray binary pulsar EXO 2030+375
• Spectral and Timing Analysis of the accretion-powered pulsar 4U 1626-67 observed with Suzaku and NuSTAR
• Energy-resolved pulse profiles of accreting pulsars: Diagnostic tools for spectral features
• 4U 1626-67 Returns to Spin-Down: Timing features toe the line
• On the torque reversals of 4U 1626--67
• The X-ray pulsar XTE J1858+034 observed with NuSTAR and Fermi/GBM: spectral and timing characterization plus a cyclotron line
• A high-mass X-ray binary pulsar 4U 1907+09 with multiple absorption-line features in the spectrum
• 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
• Swift unveils the orbital period of IGR J18214-1318
• The ongoing spin-down episode of 4U 1626-67
• Spectro-timing analysis of Be X-ray pulsar SMC X-2 during the 2022 outburst
• The NuSTAR view of Ultra-Compact X-ray Binaries
• Chandra/LETGS Studies of the Collisional Plasma in 4U 1626-67