We use 3D computer modelling to investigate the timescales and radiative output from maser flares generated by the impact of shock-waves on astronomical unit-scale clouds in interstellar and star-forming regions, and in circumstellar regions in some circumstances. Physical conditions are derived from simple models of isothermal hydrodynamic (single-fluid) and C-type (ionic and neutral fluid) shock-waves, and based on the ortho-H2O 22-GHz transition. Maser saturation is comprehensively included, and we find that the most saturated maser inversions are found predominantly in the shocked material. We study the effect on the intensity, flux density and duration of flares of the following parameters: the pre-shock level of saturation, the observer’s viewpoint, and the shock speed. Our models are able to reproduce observed flare rise times of a few times 10 days, specific intensities of up to 105 times the saturation intensity and flux densities of order 100(R/d)2 Jy from a source of radius R astronomical units at a distance of d kiloparsec. We found that flares from C-type shocks are approximately 5 times more likely to be seen by a randomly placed observer than flares from hydrodynamically shocked clouds of similar dimensions. We computed intrinsic beaming patterns of the maser emission, finding substantial extension of the pattern parallel to the shock front in the hydrodynamic models. Beaming solid angles for hydrodynamic models can be as small as 1.3 × 10−5 sr, but are an order of magnitude larger for C-type models.

中文翻译：

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由等温冲击波驱动的脉泽耀斑

我们使用 3D 计算机建模来研究冲击波对星际和恒星形成区域以及某些情况下的星周区域的天文单位尺度云的冲击所产生的脉泽耀斑的时间尺度和辐射输出。物理条件源自等温流体动力学（单流体）和 C 型（离子和中性流体）冲击波的简单模型，并基于 ortho-H2O 22 GHz 跃迁。脉泽饱和度被全面包括在内，我们发现最饱和的脉泽反演主要出现在冲击材料中。我们研究以下参数对耀斑强度、通量密度和持续时间的影响：预震饱和度、观察者的视点和冲击速度。我们的模型能够重现观测到的耀斑上升时间为 10 天数倍，特定强度高达饱和强度的 105 倍，通量密度为 100(R/d)2 Jy，来自半径为 R 天文单位的源，在d 千秒差距的距离。我们发现，随机放置的观察者看到 C 型激波产生的耀斑的可能性大约是类似尺寸的流体动力冲击云产生的耀斑的 5 倍。我们计算了脉泽发射的固有波束模式，发现波束模式在流体动力学模型中平行于激波前沿的大量延伸。流体动力学模型的波束立体角可小至 1.3 × 10−5 sr，但 C 型模型的波束立体角要大一个数量级。