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Constraints on the Neutron Star and Inner Accretion Flow in Serpens X-1 Using NuSTAR

Miller, J. M. and Parker, M. L. and Fuerst, F. and Bachetti, M. and Barret, D. and Grefenstette, B. W. and Tendulkar, S. and Harrison, F. A. and Boggs, S. E. and Chakrabarty, D. and Christensen, F. E. and Craig, W. W. and Fabian, A. C. and Hailey, C. J. and Natalucci, L. and Paerels, F. and Rana, V. and Stern, D. K. and Tomsick, J. A. and Zhang, W. W. (2013) Constraints on the Neutron Star and Inner Accretion Flow in Serpens X-1 Using NuSTAR. Astrophysical Journal Letters, 779 (1). Art. No. L2. ISSN 2041-8205. http://resolver.caltech.edu/CaltechAUTHORS:20140108-080908162

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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.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://iopscience.iop.org/2041-8205/779/1/L2/PublisherArticle
http://dx.doi.org/10.1088/2041-8205/779/1/L2DOIArticle
http://arxiv.org/abs/1310.5776arXivDiscussion Paper
ORCID:
AuthorORCID
Bachetti, M.0000-0002-4576-9337
Harrison, F. A.0000-0003-2992-8024
Boggs, S. E.0000-0001-9567-4224
Rana, V.0000-0003-1703-8796
Stern, D. K.0000-0003-2686-9241
Additional Information:© 2013 American Astronomical Society. Received 2013 October 2; accepted 2013 October 18; published 2013 November 21. This work was supported under NASA Contract No. NNG08FD60C, and made use of data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA.
Group:NuSTAR, Space Radiation Laboratory
Funders:
Funding AgencyGrant Number
NASANNG08FD60C
NASA/JPL/CaltechUNSPECIFIED
Subject Keywords:accretion, accretion disks; equation of state; relativistic processes; X-rays: binaries
Record Number:CaltechAUTHORS:20140108-080908162
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20140108-080908162
Official Citation:Constraints on the Neutron Star and Inner Accretion Flow in Serpens X-1 Using NuSTAR J. M. Miller et al. 2013 ApJ 779 L2
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:43257
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:08 Jan 2014 16:32
Last Modified:02 Oct 2017 20:20

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