We report the results of AstroSat observations of GRS 1915$+$105 obtained using 100 ks guaranteed-time (GT) during the soft state. The Color-Color Diagram (CCD) indicates a variability class of $\delta$ with the detection of High Frequency QPO (HFQPO) in the power density spectra (PDS). The HFQPO is seen to vary in the frequency range of $67.96 - 70.62$ Hz with percentage rms $\sim 0.83 - 1.90$ % and significance varying from $1.63 - 7.75$. The energy dependent power spectra show that the HFQPO features are dominant only in $6 - 25$ keV energy band. The broadband energy spectra ($0.7 - 50$ keV) of SXT (Soft X-ray Telescope) and LAXPC (Large Area X-ray Proportional Counter) modelled with nthComp and powerlaw imply that the source has an extended corona in addition to a compact 'Comptonizing corona' that produces high energy emission and exhibits HFQPOs. The broadband spectral modelling indicates that the source spectra are well described by thermal Comptonization with electron temperature (kT$_{\rm e}$) of $2.07 - 2.43$ keV and photon-index ($\Gamma_{\rm nth}$) between $1.73-2.45$ with an additional powerlaw component of photon-index ($\Gamma_{\rm PL}$) between $2.94 - 3.28$. The norm of nthComp component is high ($\sim 8$) during the presence of strong HFQPO and low ($\sim 3$) during the absence of HFQPO. Further, we model the energy spectra with the kerrbb model to estimate the accretion rate, mass and spin of the source. Our findings indicate that the source accretes at super-Eddington rate of $1.17-1.31~ \dot{M}_{\rm Edd}$. Moreover, we find the mass and spin of the source as $12.44 - 13.09~M_{\odot}$ and $0.990-0.997$ with $90\%$ confidence suggesting that GRS 1915$+$105 is a maximally rotating stellar mass X-ray binary black hole source.

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软状态期间 GRS 1915+105 的 AstroSat 视图：HFQPO 的检测和质量和自旋的估计

我们报告了在软状态期间使用 100 ks 保证时间 (GT) 获得的 GRS 1915$+$105 的 AstroSat 观测结果。在功率密度谱 (PDS) 中检测到高频 QPO (HFQPO) 时，颜色-颜色图 (CCD) 指示了 $\delta$ 的可变性类别。HFQPO 被视为在 $67.96 - 70.62$ Hz 的频率范围内变化，百分比 rms $\sim 0.83 - 1.90$ % 和显着性在 $1.63 - 7.75$ 之间变化。能量相关功率谱表明 HFQPO 特征仅在 $6 - 25 $ keV 能带中占主导地位。使用 nthComp 和幂律建模的 SXT（软 X 射线望远镜）和 LAXPC（大面积 X 射线比例计数器）的宽带能谱（0.7 美元 - 50 美元 keV）意味着除了紧凑的补偿电晕' 产生高能量发射并表现出HFQPO。宽带光谱模型表明，源光谱可以通过热补偿很好地描述，电子温度 (kT$_{\rm e}$) 为 $2.07 - 2.43$ keV 和光子指数 ($\Gamma_{\rm nth}$)在 $1.73-2.45$ 之间，光子指数的附加幂律分量 ($\Gamma_{\rm PL}$) 在 $2.94 - 3.28$ 之间。在强 HFQPO 存在期间，nthComp 分量的范数较高（$\sim 8$），而在没有 HFQPO 的情况下，其范数较低（$\sim 3$）。此外，我们使用 kerrbb 模型对能谱进行建模，以估计源的吸积率、质量和自旋。我们的研究结果表明，源以 $1.17-1.31~\dot{M}_{\rm Edd}$ 的超爱丁顿速度增加。此外，我们发现源的质量和自旋为 $12.44 - 13.09~M_{\odot}$ 和 $0.990-0。