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|a Ludlam, RM
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|a Jaodand, AD
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|a García, JA
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|a Degenaar, N
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|a Tomsick, JA
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|a Cackett, EM
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|a Fabian, AC
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|a Gandhi, P
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|a Buisson, DJK
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|a Shaw, AW
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|a Chakrabarty, D
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|a Simultaneous NICER and NuSTAR Observations of the Ultracompact X-Ray Binary 4U 1543-624
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|b American Astronomical Society,
|c 2022-03-31T12:46:08Z.
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|z Get fulltext
|u https://hdl.handle.net/1721.1/141429
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|a <jats:title>Abstract</jats:title> <jats:p>We present the first joint NuSTAR and NICER observations of the ultracompact X-ray binary (UCXB) 4U 1543−624 obtained in 2020 April. The source was at a luminosity of <jats:italic>L</jats:italic> <jats:sub>0.5−50 keV</jats:sub> = 4.9(<jats:italic>D</jats:italic>/7 kpc)<jats:sup>2</jats:sup> × 10<jats:sup>36</jats:sup> erg s<jats:sup>−1</jats:sup> and showed evidence of reflected emission in the form of an O <jats:sc>viii</jats:sc> line, Fe K line, and Compton hump within the spectrum. We used a full reflection model, known as <jats:sc>xillverCO</jats:sc>, that is tailored for the atypical abundances found in UCXBs, to account for the reflected emission. We tested the emission radii of the O and Fe line components and conclude that they originate from a common disk radius in the innermost region of the accretion disk (<jats:italic>R</jats:italic> <jats:sub>in</jats:sub> ≤ 1.07 <jats:italic>R</jats:italic> <jats:sub>ISCO</jats:sub>). Assuming that the compact accretor is a neutron star (NS) and the position of the inner disk is the Alfvén radius, we placed an upper limit on the magnetic field strength to be <jats:italic>B</jats:italic> ≤ 0.7(<jats:italic>D</jats:italic>/7 kpc) × 10<jats:sup>8</jats:sup> G at the poles. Given the lack of pulsations detected and position of <jats:italic>R</jats:italic> <jats:sub>in</jats:sub>, it was likely that a boundary layer region had formed between the NS surface and inner edge of the accretion disk with an extent of 1.2 km. This implies a maximum radius of the neutron star accretor of <jats:italic>R</jats:italic> <jats:sub>NS</jats:sub> ≤ 12.1 km when assuming a canonical NS mass of 1.4 <jats:italic>M</jats:italic> <jats:sub>⊙</jats:sub>.</jats:p>
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|a en
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|a Article
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|t 10.3847/1538-4357/ABEDB0
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|t Astrophysical Journal
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