We performed spectro-temporal analysis in the 0.8--50 keV energy band of the neutron star Z source GX 17+2 using AstroSat Soft X-ray Telescope (SXT) and Large Area X-ray Proportional Counter (LAXPC) data. The source was found to vary in the normal branch of the Hardness Intensity Diagram. Cross-correlation studies of LAXPC light curves in soft and hard X-ray band unveiled anticorrelated lags of the order of few hundred seconds. For the first time, Cross-correlation studies were performed using SXT soft and LAXPC hard lightcurves and they exhibited correlated and anti-correlated lags of the order of a hundred seconds. Power density spectrum displayed NB oscillations of 6.7--7.8 Hz (quality factor 1.5--4.0). Spectral modeling resulted in inner disk radius of $\sim$ 12--16 km with $\Gamma$ $\sim$ 2.31--2.44 indicating that disk is close to the ISCO and a similar value of disk radius was noticed based on the reflection model. Different methods were used to constrain the corona size in GX 17+2. Using the detected lags, corona size was found to be 27-46 km ($\beta$ = 0.1, $\beta$ = v$_{corona}$/v$_{disk}$) and 138--231 km ($\beta$ = 0.5). Assuming the X-ray emission to be arising from the Boundary Layer (BL), its size was determined to be 57--71 km. Assuming that BL is ionizing the disk's inner region, it's size was constrained to $\sim$ 19--86 km. Using NBO frequency, the transition shell radius was found to be around 32 km. Observed lags and no movement of the inner disk front strongly indicates that the varying corona structure is causing the X-ray variation in the NB of Z source GX 17+2.

中文翻译：

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GX 17+2 正常分支的日冕垂直结构变化：AstroSat 的 SXT 和 LAXPC 视角

我们使用 AstroSat 软 X 射线望远镜 (SXT) 和大面积 X 射线比例计数器 (LAXPC) 数据对中子星 Z 源 GX 17+2 的 0.8--50 keV 能带进行了光谱时间分析。发现源在硬度强度图的正常分支中有所不同。软和硬 X 射线波段中 LAXPC 光曲线的互相关研究揭示了几百秒数量级的反相关滞后。首次使用 SXT 软光曲线和 LAXPC 硬光曲线进行互相关研究，它们表现出数百秒数量级的相关和反相关滞后。功率密度谱显示 NB 振荡为 6.7--7.8 Hz（品质因数 1.5--4.0）。光谱建模导致内盘半径为 $\sim$ 12--16 km，$\Gamma$ $\sim$ 为 2.31--2。44 表明磁盘接近 ISCO 并且基于反射模型注意到磁盘半径的相似值。使用不同的方法来限制 GX 17+2 中的电晕尺寸。使用检测到的滞后，发现电晕大小为 27-46 公里（$\beta$ = 0.1，$\beta$ = v$_{corona}$/v$_{disk}$）和 138--231 公里（$\beta$ = 0.5）。假设 X 射线发射来自边界层 (BL)，它的大小被确定为 57--71 公里。假设 BL 正在电离磁盘的内部区域，它的大小被限制在 $\sim$ 19--86 km。使用 NBO 频率，发现过渡壳半径约为 32 公里。观察到的滞后和内部盘面没有运动强烈表明变化的日冕结构正在导致 Z 源 GX 17+2 NB 中的 X 射线变化。