THE SPECTRAL EVOLUTION ALONG THE Z TRACK OF THE BRIGHT NEUTRON STAR X-RAY BINARY GX 17+2
THE SPECTRAL EVOLUTION ALONG THE Z TRACK OF THE BRIGHT NEUTRON STAR X-RAY BINARY GX 17+2
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DOI：
10.1088/0004-637x/756/1/34
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发表时间：
2012-07
期刊：
影响因子：
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通讯作者：
D. Lin;R. Remillard;J. Homan;D. Barret
中科院分区：
文献类型：
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作者：
D. Lin;R. Remillard;J. Homan;D. Barret
Z源是明亮的中子星x射线双星，在爱丁顿极限附近吸积。我们分析了1999年10月3日至12日期间的68次RXTE观测（~ 270 ks），覆盖了完整的Z轨道。我们用一个由热多色盘、单一温度黑体边界层和弱复合组分组成的模型建立并拟合了颜色分辨光谱。我们发现，与XTE J1701-462的co-样Z相相似，GX 17+2的分支可以解释为以恒定吸积速率运行的三个过程：在水平分支（HB）上的复杂化增加，在正常分支（NB）上从标准薄盘过渡到薄盘，以及在扩张分支上的内盘半径暂时快速减小。我们还以经验自一致的方式模拟了复合化，将其种子光子与热盘分量绑定并进行校正以恢复预复合化的热盘发射。这允许我们显示一个常数沿着整个Z轨道基于热盘组件。我们还测量了上千赫准周期振荡频率，发现它与内盘半径Rin（在康普顿散射之前）的关系近似为频率∝R−3/2in，支持将其识别为Rin处的开普勒频率。HB振荡也可能与内盘的动力学有关，因为它的频率和Rin在HB上变化很大，但在NB上相对恒定。
Z sources are bright neutron star X-ray binaries, accreting at around the Eddington limit. We analyze the 68 RXTE observations (∼270 ks) of Sco-like Z source GX 17+2 made between 1999 October 3 and 12, covering a complete Z track. We create and fit color-resolved spectra with a model consisting of a thermal multicolor disk, a single-temperature-blackbody boundary layer and a weak Comptonized component. We find that, similar to what was observed for XTE J1701-462 in its Sco-like Z phase, the branches of GX 17+2 can be explained by three processes operating at a constant accretion rate into the disk: increase of Comptonization up the horizontal branch (HB), transition from a standard thin disk to a slim disk up the normal branch (NB), and temporary fast decrease of the inner disk radius up the flaring branch. We also model the Comptonization in an empirically self-consistent way, with its seed photons tied to the thermal disk component and corrected for to recover the pre-Comptonized thermal disk emission. This allows us to show a constant along the entire Z track based on the thermal disk component. We also measure the upper kHz quasi-periodic oscillation frequency and find it to depend on the apparent inner disk radius Rin (prior to Compton scattering) approximately as frequency ∝ R−3/2in, supporting the identification of it as the Keplerian frequency at Rin. The HB oscillation is probably related to the dynamics in the inner disk as well, as both its frequency and Rin vary significantly on the HB but become relatively constant on the NB.