Short-term variability of x-rays from accreting neutron star vela X-1. I. Suzaku observations
Short-term variability of x-rays from accreting neutron star vela X-1. I. Suzaku observations
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吸积中子星帆 X-1 发出的 X 射线的短期变化。
DOI：
10.1088/0004-637x/767/1/70
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发表时间：
2013
影响因子：
4.9
通讯作者：
K.
中科院分区：
文献类型：
--
作者：
Odaka;H.;Khangulyan;D.;Tanaka;Y.T.;Watanabe;S.;Takahashi;T.;Makishima;K.
利用100 ks曝光量的朱雀观测资料，分析了最亮的风馈吸积中子星星船帆座X-1的宽波段X射线谱在2 ks短时间尺度上的时变。在观测过程中，该天体表现出很强的可变性，包括几次耀斑和所谓的”低态”，其中X射线光度降低了一个数量级。虽然光谱硬度随着X射线光度的增加而增加，但大多数记录的耀斑在星周吸收方面没有显示出任何显着的变化。然而，在一次短暂的耀斑出现之前，就有大量吸收的迹象，显示出显着的光谱硬化。在低状态下，流量水平调制脉冲星的自旋周期，表明即使在这种状态下的吸积流达到中子星星的紧密接近。从现象学上讲，宽带X射线光谱，这是集成在整个自旋阶段，很好地代表了“NPEX”功能（负和正的幂律与指数截止由一个共同的折叠能量的组合）与回旋共振散射功能在50千电子伏。拟合的数据使我们能够推断光子指数和X射线光度之间的相关性。最后，星周吸收显示出轨道相位间隔0.25-0.3的逐渐增加，这可以解释为在超音速恒星风中的紧凑物体的运动所施加的弓形激波的影响。
We have analyzed the time variability of the wide-band X-ray spectrum of Vela X-1, the brightest wind-fed accreting neutron star, on a short timescale of 2 ks by using Suzaku observations with an exposure of 100 ks. During the observation, the object showed strong variability, including several flares and so-called" low states," in which the X-ray luminosity decreases by an order of magnitude. Although the spectral hardness increases with the X-ray luminosity, the majority of the recorded flares do not show any significant changes in circumstellar absorption. However, a sign of heavy absorption was registered immediately before one short flare that showed a significant spectral hardening. In the low states, the flux level is modulated with the pulsar spin period, indicating that even at this state the accretion flow reaches the close proximity of the neutron star. Phenomenologically, the broadband X-ray spectra, which are integrated over the entire spin phase, are well represented by the" NPEX" function (a combination of negative and positive power laws with an exponential cutoff by a common folding energy) with a cyclotron resonance scattering feature at 50 keV. Fitting of the data allowed us to infer a correlation between the photon index and X-ray luminosity. Finally, the circumstellar absorption shows a gradual increase in the orbital phase interval 0.25–0.3, which can be interpreted as an impact of a bow shock imposed by the motion of the compact object in the supersonic stellar wind.