The Be X-ray binary EXO 2030+375 went through its third recorded giant outburst from June 2021 to early 2022. We present the results of both spectral and timing analysis based on NICER monitoring, covering the 2−10 keV flux range from 20 to 310 mCrab. Dense monitoring with observations carried out about every second day and a total exposure time of ∼160 ks allowed us to closely track the source evolution over the outburst. Changes in the spectral shape and pulse profiles showed a stable luminosity dependence during the rise and decline. The same type of dependence has been seen in past outbursts. The pulse profile is characterized by several distinct peaks and dips. The profiles show a clear dependence on luminosity with a stark transition at a luminosity of ∼2 × 10^{36 erg s−1, indicating a change in the emission pattern. Using relativistic raytracing, we demonstrate how anisotropic beaming of emission from an accretion channel with a constant geometrical configuration can give rise to the observed pulse profiles over a range of luminosities.}

中文翻译：

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EXO 2030+375的巨型爆发


Be X 射线双星 EXO 2030+375 从 2021 年 6 月到 2022 年初经历了第三次有记录的巨大爆发。我们展示了基于 NICER 监测的光谱和时间分析结果，涵盖了从 20 到 20 的 2−10 keV 通量范围。 310 米螃蟹。大约每隔一天进行一次密集监测和观测，总曝光时间约为 160 ks，使我们能够密切跟踪爆发期间的源演化。光谱形状和脉冲轮廓的变化在上升和下降过程中表现出稳定的光度依赖性。在过去的爆发中也曾出现过同样类型的依赖。脉冲轮廓的特征在于几个不同的峰和谷。轮廓显示出对光度的明显依赖性，在光度为~2 × 10 ^{36 erg s -1 时出现明显的转变，表明发射模式发生了变化。使用相对论光线追踪，我们演示了来自具有恒定几何配置的吸积通道的各向异性发射光束如何在一定光度范围内产生观察到的脉冲轮廓。}