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arXiv 2107.04048astro-ph.HE
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致密CSM冲击击穿和冷却的解析光变曲线

Analytic Light Curves of Dense CSM Shock Breakout and Cooling

Ben Margalit

摘要:

致密的拱星物质(CSM)被认为在观测到的发光光学瞬变中起着重要的作用:如果这样的CSM受到冲击,例如在核心坍缩期间从祖星喷出的喷出物,那么由冲击加热的CSM产生的辐射可以为明亮的UV/光学发射提供动力。如果初始CSM有一个“外边缘”,其中包含大部分质量,并且光学深度很大,那么冲击爆发-当光子首先能够逃离冲击CSM时-发生在这个外边缘附近。受冲击CSM的$\sim$薄壳随后膨胀,并且在随后的冷却包层阶段,辐射和绝热损失竞争消耗CSM的热能。在这里,我们推导出一个解析解的辐射热光变曲线所产生的冲击CSM。对于第一次,我们提供了一个解析解的冷却包线阶段,适用于从冲击爆发,直到扩大CSM变得光学薄。特别是,我们占的平面CSM的几何形状是相关的,在早期和适当地处理在这个平面阶段的辐射损失。我们表明,这些影响可以显着影响由此产生的光变曲线,特别是如果CSM光学深度仅略大于$c/v_{\rm sh}$(其中$v_{\rm sh}$是冲击速度)。这对于解释观察到的快速光学瞬态具有重要意义,这些瞬态以前已经使用计算昂贵的数值模拟或更简化的模型进行建模,这些模型不能正确捕获早期光变曲线的演变。

英文摘要:

Dense circumstellar material (CSM) is thought to play an important role in observed luminous optical transients: if such CSM is shocked, e.g. by ejecta expelled from the progenitor during core-collapse, then radiation produced by the shock-heated CSM can power bright UV/optical emission. If the initial CSM has an `outer edge' where most of the mass is contained and at which the optical depth is large, then shock breakout -- when photons are first able to escape the shocked CSM -- occurs near this outer edge. The $\sim$thin shell of shocked CSM subsequently expands, and in the ensuing cooling-envelope phase, radiative and adiabatic losses compete to expend the CSM thermal energy. Here we derive an analytic solution to the bolometric light-curve produced by such shocked CSM. For the first time, we provide an analytic solution to the cooling-envelope phase that is applicable starting from shock-breakout and until the expanding CSM becomes optically-thin. In particular, we account for the planar CSM geometry that is relevant at early times and properly treat radiative losses within this planar phase. We show that these effects can dramatically impact the resulting light-curves, particularly if the CSM optical depth is only marginally larger than $c/v_{\rm sh}$ (where $v_{\rm sh}$ is the shock velocity). This has important implications for interpreting observed fast optical transients, which have previously been modeled using either computationally-expensive numerical simulations or more simplified models that do not properly capture the early light-curve evolution.

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