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Published September 11, 2017 | Accepted Version
Journal Article Open

A broad-band 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 broad-band spectrum are similar to those of X-ray pulsars hosted in a high-mass X-ray binary system, with a broad resonant cyclotron scattering feature (CRSF) at ∼37 keV. In this work, we examine the pulse-resolved and the pulse-averaged broad-band 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 broad-band model for the disc-reflected spectrum. In the softer X-ray band, we need to add a soft blackbody component with kT_(bb) ∼ 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 ∼61 keV.

Additional Information

© 2017 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2017 May 8. Received 2017 May 7; in original form 2016 December 28. Published: 11 May 2017. AD acknowledges contract ASI-INAF I/004/11/0.We acknowledge the NASA High Energy Astrophysics Science Archive Research Center (HEASARC) for developing and maintaining the HEASOFT software that has been used in this study.

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August 19, 2023
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