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arXiv · 1705.03404

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

Antonino D'Aì·Giancarlo Cusumano·Melania Del Santo·Valentina La Parola·Alberto Segreto
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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 $kT_{\rm bb}$ $\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.

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Antonino D'Aì, Giancarlo Cusumano, Melania Del Santo, Valentina La Parola, Alberto Segreto. 2017-05-09. A broadband self-consistent modelling of the X-ray spectrum of 4U 1626--67. https://doi.org/10.1093/mnras%2Fstx1146

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