A NuSTAR observation of disc reflection from close to the neutron star in 4U 1608-52
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A NuSTAR observation.pdf
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Author(s)
Degenaar, N.
Miller, J. M.
Harrison, F. A.
Kara, E.
Fabian, A. C.
Chakrabarty, Deepto
Date Issued
May 2015
Journal
Monthly Notices of the Royal Astronomical Society Letters
Publisher
Oxford University Press
Citation
Degenaar, N.; Miller, J. M.; Chakrabarty, D.; Harrison, F. A.; Kara, E. and Fabian, A. C. “A NuSTAR Observation of Disc Reflection from Close to the Neutron Star in 4U 1608-52.” Monthly Notices of the Royal Astronomical Society: Letters 451, no. 1 (June 2015): L85–L89. © 2015 The Authors
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Author's final manuscript
Abstract
Studying the reflection of X-rays off the inner edge of the accretion disc in a neutron star low-mass X-ray binary allows us to investigate the accretion geometry and to constrain the radius of the neutron star. We report on a NuSTAR observation of 4U 1608–52 obtained during a faint outburst in 2014 when the neutron star, which has a known spin frequency of ν = 620 Hz, was accreting at ≃1–2 per cent of the Eddington limit. The 3–79 keV continuum emission was dominated by a Γ ≃ 2 power law, with an ≃1–2 per cent contribution from a kTbb ≃ 0.3–0.6 keV blackbody component. The high-quality NuSTAR spectrum reveals the hallmarks of disc reflection; a broad iron-line peaking near 7 keV and a Compton back-scattering hump around ≃20–30 keV. Modelling the disc reflection spectrum points to a binary inclination of i ≃30°–40° and a small ‘coronal’ height of h ≲8.5GM/c2. Furthermore, our spectral analysis suggests that the inner disc radius extended to Rin ≃ 7–10GM/c2, close to the innermost stable circular orbit. This constrains the neutron star radius to R ≲21 km and the redshift from the stellar surface to z ≳0.12, for a mass of M = 1.5 M⊙ and a spin parameter of a = 0.29.
MIT Department
Massachusetts Institute of Technology. Department of Physics
MIT Kavli Institute for Astrophysics and Space Research
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DOI of Published Version
https://doi.org/10.1093/mnrasl/slv072
