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A NuSTAR observation of disc reflection from close to the neutron star in 4U 1608–52

Degenaar, N. and Miller, J. M. and Chakrabarty, D. and Harrison, F. A. and Kara, E. and Fabian, A. C. (2015) A NuSTAR observation of disc reflection from close to the neutron star in 4U 1608–52. Monthly Notices of the Royal Astronomical Society, 451 (1). L85-L89. ISSN 0035-8711. doi:10.1093/mnrasl/slv072.

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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 kT_(bb) ≃ 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/c^2. Furthermore, our spectral analysis suggests that the inner disc radius extended to R_(in) ≃ 7–10GM/c^2, 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.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper DOIArticle
Chakrabarty, D.0000-0001-8804-8946
Harrison, F. A.0000-0003-2992-8024
Kara, E.0000-0003-0172-0854
Fabian, A. C.0000-0002-9378-4072
Additional Information:© 2015 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2015 May 8. Received 2015 May 8. In original form 2015 April 2. First published online June 10, 2015. We thank the referee, Craig Heinke, for thoughtful comments. ND acknowledges support via an EU Marie Curie Intra-European fellowship under contract no. FP-PEOPLE-2013-IEF-627148. This work is based on data from the NuSTAR mission, a project led by California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA. We thank Neil Gehrels and the Swift team for rapid scheduling of observations.
Group:NuSTAR, Space Radiation Laboratory
Funding AgencyGrant Number
Marie Curie FellowshipFP-PEOPLE-2013-IEF-627148
Subject Keywords:accretion, accretion discs – stars: individual: 4U 1608–52 – stars: neutron – X-rays: binaries
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Space Radiation Laboratory2015-07
Issue or Number:1
Record Number:CaltechAUTHORS:20150802-162212946
Persistent URL:
Official Citation:N. Degenaar, J. M. Miller, D. Chakrabarty, F. A. Harrison, E. Kara, and A. C. Fabian A NuSTAR observation of disc reflection from close to the neutron star in 4U 1608–52 MNRAS (July 21, 2015) Vol. 451 L85-L89 doi:10.1093/mnrasl/slv072 First published online June 10, 2015
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:59142
Deposited By: Joy Painter
Deposited On:05 Aug 2015 23:55
Last Modified:10 Nov 2021 22:15

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