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Title: Constraints on the Neutron Star and Inner Accretion Flow in Serpens X-1 Using NuSTAR
Authors: Miller, J. M.
Parker, M. L.
Rana, V
+17 Co-Authors
Keywords: accretion
accretion disks
equation of state
relativistic processes
X-rays: binaries
Issue Date: 10-Dec-2013
Publisher: IOP Sciences for American Astronomical Society
Citation: The Astrophysical Journal Letters, 2013, Vol.779, p6
Abstract: We report on an observation of the neutron star low-mass X-ray binary Serpens X-1, made with NuSTAR. The extraordinary sensitivity afforded by NuSTAR facilitated the detection of a clear, robust, relativistic Fe K emission line from the inner disk. A relativistic profile is required over a single Gaussian line from any charge state of Fe at the 5σ level of confidence, and any two Gaussians of equal width at the same confidence. The Compton back-scattering "hump" peaking in the 10-20 keV band is detected for the first time in a neutron star X-ray binary. Fits with relativistically blurred disk reflection models suggest that the disk likely extends close to the innermost stable circular orbit (ISCO) or stellar surface. The best-fit blurred reflection models constrain the gravitational redshift from the stellar surface to be z NS ≥ 0.16. The data are broadly compatible with the disk extending to the ISCO; in that case, z NS ≥ 0.22 and R NS ≤ 12.6 km (assuming M NS = 1.4 M ☉ and a = 0, where a = cJ/GM 2). If the star is as large or larger than its ISCO, or if the effective reflecting disk leaks across the ISCO to the surface, the redshift constraints become measurements. We discuss our results in the context of efforts to measure fundamental properties of neutron stars, and models for accretion onto compact objects.
Description: Open Access.
ISSN: 0004-637X
1538-4357 (online)
Alternative Location:
Copyright: 2013 The American Astronomical Society.
Appears in Collections:Research Papers (A&A)

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