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Published August 20, 2016 | Submitted + Published
Journal Article Open

A NuSTAR Observation of the Reflection Spectrum of the Low-mass X-Ray Binary 4U 1728-34

Abstract

We report on a simultaneous NuSTAR and Swift observation of the neutron star low-mass X-ray binary 4U 1728-34. We identified and removed four Type I X-ray bursts during the observation in order to study the persistent emission. The continuum spectrum is hard and described well by a blackbody with kT = 1.5 keV and a cutoff power law with Γ = 1.5, and a cutoff temperature of 25 keV. Residuals between 6 and 8 keV provide strong evidence of a broad Fe Kα line. By modeling the spectrum with a relativistically blurred reflection model, we find an upper limit for the inner disk radius of R_(in) ⩽ 2R_(ISCO). Consequently, we find that R_(NS) ⩽ 23 km, assuming M = 1.4 M_⊙ and a = 0.15. We also find an upper limit on the magnetic field of B ⩽ 2 × 10^8 G.

Additional Information

© 2016 The American Astronomical Society. Received 2016 February 9; revised 2016 June 17; accepted 2016 June 25; published 2016 August 18. We thank Michael Parker and Andy Fabian for the particular version of the reflionx model used in this analysis. We thank Kristin Madsen for her help identifying the calibration issue in the NuSTAR data between 3–4.5 keV. J.C. thanks ESA/PRODEX for financial support. This work is based on data from the NuSTAR mission, a project led by the California Institute of Technology, managed by the Jet Propulsion Laboratory, and funded by NASA.

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Published - apj_827_2_134.pdf

Submitted - 1605.02137v2.pdf

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August 20, 2023
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