Evidence for the Photoionization Absorption Edge in a Photospheric Radius Expansion X-Ray Burst from GRS 1747–312 in Terzan 6
Evidence for the Photoionization Absorption Edge in a Photospheric Radius Expansion X-Ray Burst from GRS 1747–312 in Terzan 6
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DOI：
10.3847/1538-4357/aade8e
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发表时间：
2018-08
期刊：
影响因子：
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通讯作者：
Z. Li;V. Suleimanov;J. Poutanen;Tuomo Salmi;M. Falanga;J. Nattila;R. Xu
中科院分区：
文献类型：
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作者：
Z. Li;V. Suleimanov;J. Poutanen;Tuomo Salmi;M. Falanga;J. Nattila;R. Xu
中子星表面的热核X射线暴可以使光球层中的金属更加丰富，这可能会在爆发谱上留下光致电离边缘。本文报道了在Rossi X射线计时探测器观测期间，在泰山6号的NS低质量X射线双星GRS1747-−-312的I型X射线爆发光谱中发现的吸收边。我们发现，在光球半径扩展阶段，边缘能量从9.45±0.51演化到∼6keV，然后又回到9.44±0.40keV，并在冷却尾部保持在8.06±0.66keV。类氢镍、铁或铁/镍混合物的光致电离吸收边和金属的束缚-束缚跃迁可能是造成观察到的光谱特征的原因。测量的冷却尾部吸收边能与类氢Ni(Fe)边能实验值之比，可以估算出引力红移因子1+z=1.34±0.11(1+z=1.15±0.09)。富金属大气模式很好地描述了冷尾过程中光谱参数的演变。直接冷却方法对NS质量和半径的综合约束以及潮汐变形性强烈地表明大气中铁族元素的丰度很高，并将距离源区的距离限制在11±1kpc。
Thermonuclear X-ray bursts on the surface of neutron stars (NSs) can enrich the photosphere with metals, which may imprint photoionization edges on the burst spectra. We report here the discovery of absorption edges in the spectra of the type I X-ray burst from the NS low-mass X-ray binary GRS 1747−312 in Terzan 6 during observations by the Rossi X-ray Timing Explorer. We find that the edge energy evolves from 9.45 ± 0.51 to ∼6 keV and then back to 9.44 ± 0.40 keV during the photospheric radius expansion phase and remains at 8.06 ± 0.66 keV in the cooling tail. The photoionization absorption edges of hydrogen-like Ni, Fe, or an Fe/Ni mixture and the bound–bound transitions of metals may be responsible for the observed spectral features. The ratio of the measured absorption edge energy in the cooling tail to the laboratory value of the hydrogen-like Ni(Fe) edge energy allows us to estimate the gravitational redshift factor 1 + z = 1.34 ± 0.11(1 + z = 1.15 ± 0.09). The evolution of the spectral parameters during the cooling tail are well described by metal-rich atmosphere models. The combined constraints on the NS mass and radius from the direct cooling method and the tidal deformability strongly suggest very high atmospheric abundance of the iron group elements and limit the distance to the source to 11 ± 1 kpc.