基于Z源GX 17+2几百秒延迟的日冕高度和重调速度约束
Constraining the Coronal Heights and Readjustment Velocities Based on the Detection of a Few Hundred Seconds Delays in the Z Source GX 17+2
摘要：
中子星Z型源提供了一个独特的平台，以了解吸积盘的结构-日冕几何发射接近爱丁顿光度。利用RXTE和NuSTAR卫星资料，对GX 17+2进行了交叉关联函数（CCF）研究，以限制产生硬X射线的日冕的大小。从RXTE数据，我们发现，在水平和正常的分支，CCF显示反相关的硬（16 - 30 keV）和软（2 - 5 keV）的X射线延迟的数量级为几十到几百秒的平均相关系数为0.42 $\pm$ 0.11。很少有观测显示相关的滞后，有一次与无线电发射一致。我们还报告了一个反相关的硬X射线延迟113 $\pm$ 51秒使用的NuSTAR数据的GX 17+2。基于RXTE数据，发现软X射线和硬X射线通量是变化的，表明在延迟期间盘冠结构的变化。我们用相对论进动模型、过渡层模型和边界层模型来控制日冕的大小。假设延迟是盘冕结构的再调整时间尺度，则日冕高度估计为$\sim$ 17- 100 km。假设截顶盘的内部区域被日冕占据，我们将日冕重调整速度（v $_{corona}$ = $β$ v $_{disk}$，其中v $_{disk}$是盘的径向速度分量）限制在$β$ =0.06-0.12的量级。这项研究表明，观测到的延迟主要取决于不同的日冕重调整速度。
英文摘要：
Neutron star Z type sources provide a unique platform in order to understand the structure of accretion disk-corona geometry emitting close to the Eddington luminosity. Using RXTE and NuSTAR satellite data, we performed cross correlation function (CCF) studies in GX 17+2 in order to constrain the size of corona responsible for hard X-rays. From the RXTE data, we found that during horizontal and normal branches, the CCFs show anti-correlated hard (16 - 30 keV) and soft (2 - 5 keV) X-ray delays of the order of a few tens to hundred seconds with a mean correlation coefficient of 0.42$\pm$0.11. Few observations shows correlated lags and on one occasion coincident with radio emission. We also report an anti-correlated hard X-ray delay of 113$\pm$51 s using the NuSTAR data of GX 17+2. Based on RXTE data, it was found that soft and hard X-ray fluxes are varying indicating the changes in the disk-corona structure during delays. We bridle the size of corona using relativistic precession, transition layer and boundary layer models. Assuming the delays to be readjustment time scale of disk-corona structure, height of the corona was estimated to be $\sim$ 17--100 km. Assuming that inner region of the truncated disk is occupied by the corona, we constrain the coronal readjustment velocities (v$_{corona}$=$β$ v$_{disk}$, where v$_{disk}$ is the radial velocity component of the disk) of the order of $β$=0.06-0.12. This study indicates that the observed delays are primarily dependent on the varying coronal readjustment velocities.
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