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arXiv 1708.09229astro-ph.HE
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Be/X射线脉冲双星EXO 2030+375的十年RXTE监测观测

Decade long RXTE monitoring observations of Be/X-ray binary pulsar EXO 2030+375

Prahlad Epili, Sachindra Naik, Gaurava K. Jaisawal, Shivangi Gupta

摘要:

利用Rossi X射线定时探测器1995 - 2011年的观测资料,对Be/X射线脉冲双星EXO 2030+375的时间和光谱进行了全面的研究,包括多次I型和2006年II型爆发。脉冲星的脉冲轮廓被发现是强烈的光度依赖。在低光度下,脉冲轮廓由主峰和次峰组成,该次峰在高光度下演变成具有显著相移的宽结构。一个狭窄而尖锐的吸收下降,也依赖于能量和光度,检测到的脉冲轮廓。脉冲轮廓的比较表明,在一个特定的光度的功能是独立的类型的X射线爆发。这表明发射几何仅仅是质量吸积率的函数。宽带能谱用部分覆盖高能截止模型和基于吸积柱中热康普顿化和体康普顿化的物理模型描述。我们没有发现任何签名的回旋共振散射功能从所有的观测获得的光谱。光谱参数的详细分析表明,根据源的光度,幂律光子指数分布在三个不同的区域。从理论上揭示了脉冲星从亚临界区到超临界区的光谱跃迁阶段。在~(2-4)x 10^37 erg/s范围内还观察到一个光子指数恒定的区域,这表明EXO 2030+375的临界光度状态。

英文摘要:

We present a comprehensive timing and spectral studies of Be/X-ray binary pulsar EXO 2030+375 using extensive Rossi X-ray Timing Explorer observations from 1995 till 2011, covering numerous Type I and 2006 Type II outbursts. Pulse profiles of the pulsar were found to be strongly luminosity dependent. At low luminosity, the pulse profile consisted of a main peak and a minor peak that evolved into a broad structure at high luminosity with a significant phase shift. A narrow and sharp absorption dip, also dependent on energy and luminosity, was detected in the pulse profile. Comparison of pulse profiles showed that the features at a particular luminosity are independent of type of X-ray outbursts. This indicates that the emission geometry is solely a function of mass accretion rate. The broadband energy spectrum was described with a partial covering high energy cutoff model as well as a physical model based on thermal and bulk Comptonization in accretion column. We did not find any signature of cyclotron resonance scattering feature in the spectra obtained from all the observations. A detailed analysis of spectral parameters showed that, depending on source luminosity, the power-law photon index was distributed in three distinct regions. It suggests the phases of spectral transition from sub-critical to super-critical regimes in the pulsar as proposed theoretically. A region with constant photon index was also observed in ~(2-4) x 10^37 erg/s range, indicating critical luminosity regime in EXO 2030+375.

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