We present the results obtained from timing and spectral studies of Be/X-ray binary pulsar EXO 2030+375 using observations with the Large Area Xenon Proportional Counters and Soft X-ray Telescope of AstroSat, at various phases of its Type-I outbursts in 2016, 2018, and 2020. The pulsar was faint during these observations as compared to earlier observations with other observatories. At the lowest luminosity of 2.5\(\times \)10\(^{35}\) erg s\(^{-1}\) in 0.5–30 keV energy range, \(\approx \)41.3 s pulsations were clearly detected in the X-ray light curves. This finding establishes the first firm detection of pulsations in EXO 2030+375 at an extremely low mass accretion rate to date. The shape of the pulse profiles is complex due to the presence of several narrow dips. Though pulsations were detected up to \(\sim \)80 keV when the source was brighter, pulsations were limited up to \(\sim \)25 keV during the third AstroSat observation at lowest source luminosity. A search for quasi-periodic oscillations in \(2\times 10^{-4}\) Hz to 10 Hz yielded a negative result. Spectral analysis of the AstroSat data showed that the spectrum of the pulsar was steep with a power-law index of \(\sim \)2. The values of photon-indices at observed low luminosities follow the known pattern in sub-critical regime of the pulsar.

我们使用 AstroSat 的大面积氙比例计数器和软 X 射线望远镜的观测，展示了从 Be/X 射线双脉冲星 EXO 2030+375 的计时和光谱研究中获得的结果，在其 I 型爆发的各个阶段2016、2018 和 2020 年。与其他天文台的早期观测相比，脉冲星在这些观测中显得微弱。在 2.5 \(\times \) 10 \(^{35}\) erg s \(^{-1}\)的最低光度在 0.5–30 keV 能量范围内，\(\approx \)在 X 射线光曲线中可以清楚地检测到 41.3 秒的脉动。这一发现确立了迄今为止首次在 EXO 2030+375 中以极低的质量吸积率检测到脉动。由于存在几个窄谷，脉冲轮廓的形状很复杂。虽然当光源较亮时检测到高达\(\sim \) 80 keV 的脉动，但在第三次 AstroSat 观测期间，在最低光源光度下，脉动被限制在\(\sim \) 25 keV。在\(2\times 10^{-4}\) Hz 到 10 Hz 中寻找准周期振荡产生了负面结果。AstroSat数据的光谱分析表明，脉冲星的光谱陡峭，幂律指数为\(\sim \)2. 观测到的低光度下的光子指数值遵循脉冲星亚临界状态下的已知模式。