A NuSTAR observation of the reflection spectrum of the low-mass X-ray binary 4U 1728-34

Journal Article · Sat Aug 20 04:00:00 EDT 2016 · Astrophysical Journal

DOI:https://doi.org/10.3847/0004-637X/827/2/134· OSTI ID:22868761

Sleator, Clio C.; Tomsick, John A.; Boggs, Steven E. ^[1]; King, Ashley L. ^[2]; Miller, Jon M. ^[3]; Bachetti, Matteo; Barret, Didier ^[4]; Chenevez, Jérôme; Christensen, Finn E. ^[5]; Craig, William W. ^[6]; Hailey, Charles J. ^[7]; Harrison, Fiona A.; Walton, Dominic J. ^[8]; Rahoui, Farid ^[9]; Stern, Daniel K. ^[10]; Zhang, William W. ^[11]

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1. Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
2. KIPAC, Stanford University, 452 Lomita Mall, Stanford, CA 94305 (United States)
3. Department of Astronomy, The University of Michigan, 500 Church Street, Ann Arbor, MI 48109-1046 (United States)
4. Universite de Toulouse, UPS-OMP, Toulouse (France)
5. DTU Space, Technical University of Denmark, Elektrovej 327-328, Lyngby (Denmark)
6. Lawrence Livermore National Laboratory, Livermore, CA (United States)
7. Columbia Astrophysics Laboratory and Department of Astronomy, Columbia University, 550 West 120th Street, New York, NY 10027 (United States)
8. Cahill Center for Astronomy and Astrophysics, California Institute of Technology, Pasadena, CA 91125 (United States)
9. European Southern Observatory, Karl Schwarzschild-Strasse 2, D-85748 Garching bei München (Germany)
10. Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109 (United States)
11. NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)

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{sub in}⩽2R{sub ISCO}. Consequently, we find that R {sub NS} ≤ 23 km, assuming M = 1.4 M {sub ⊙} and a = 0.15. We also find an upper limit on the magnetic field of B ≤ 2 × 10{sup 8} G.

• OSTI ID: 22868761
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 827; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCRETION DISKS
BINARY STARS
COMPUTERIZED SIMULATION
EMISSION
KEV RANGE 10-100
MAGNETIC FIELDS
MASS
NEUTRON STARS
REFLECTION
SPECTRA
X RADIATION