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NICER–NuSTAR Observations of the Neutron Star Low-mass X-Ray Binary 4U 1735–44
The Astrophysical Journal ( IF 4.9 ) Pub Date : 2020-05-22 , DOI: 10.3847/1538-4357/ab89a6
R. M. Ludlam 1 , E. M. Cackett 2 , J. A. Garca 1, 3 , J. M. Miller 4 , P. M. Bult 5, 6 , T. E. Strohmayer 6 , S. Guillot 7, 8 , G. K. Jaisawal 9 , C. Malacaria 10, 11 , A. C. Fabian 12 , C. B. Markwardt 6
Affiliation  

We report on the first simultaneous $NICER$ and $NuSTAR$ observations of the neutron star (NS) low-mass X-ray binary 4U 1735$-$44, obtained in 2018 August. The source was at a luminosity of $\sim1.8~(D/5.6\ \mathrm{kpc})^{2}\times10^{37}$ ergs s$^{-1}$ in the $0.4-30$ keV band. We account for the continuum emission with two different continuum descriptions that have been used to model the source previously. Despite the choice in continuum model, the combined passband reveals a broad Fe K line indicative of reflection in the spectrum. In order to account for the reflection spectrum we utilize a modified version of the reflection model RELXILL that is tailored for thermal emission from accreting NSs. Alternatively, we also use the reflection convolution model of RFXCONV to model the reflected emission that would arise from a Comptonized thermal component for comparison. We determine that the innermost region of the accretion disk extends close to the innermost stable circular orbit ($R_{\mathrm{ISCO}}$) at the 90% confidence level regardless of reflection model. Moreover, the current flux calibration of $NICER$ is within 5% of the $NuSTAR$/FPMA(B).

中文翻译:

NICER-NuSTAR 对中子星低质量 X 射线双星 4U 1735-44 的观测

我们报告了对 2018 年 8 月获得的中子星 (NS) 低质量 X 射线双星 4U 1735$-$44 的首次同步 $NICER$ 和 $NuSTAR$ 观测。光源的光度为 $\sim1.8~(D/5.6\\mathrm{kpc})^{2}\times10^{37}$ ergs s$^{-1}$ 在 $0.4-30$ keV 波段。我们使用两种不同的连续介质描述来解释连续介质发射,这些描述先前已用于对源进行建模。尽管选择了连续介质模型,但组合通带显示了一条宽的 Fe K 线,表明光谱中的反射。为了说明反射光谱,我们使用了反射模型 RELXILL 的修改版本,该模型专为吸积 NS 的热辐射而定制。或者,我们还使用 RFXCONV 的反射卷积模型来模拟由 Comptonized 热组件产生的反射发射以进行比较。我们确定吸积盘的最内部区域以 90% 的置信度接近最内部的稳定圆形轨道 ($R_{\mathrm{ISCO}}$),而不管反射模型如何。此外,$NICER$ 的当前通量校准在 $NuSTAR$/FPMA(B) 的 5% 以内。
更新日期:2020-05-22
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