AI 中文总结
本研究用Cloudy建模黑洞X射线双星V404 Cygni的星云阶段，再现关键观测特征，支持该阶段由团块状部分电离抛射物产生的场景。
AI 中文摘要
一些银河系中最极端的黑洞暂现源在爆发末期会呈现星云阶段。该阶段首次在V404 Cygni的2015年爆发中被确认，当时它主导了约4天的光学光谱。其特征是极强的光学发射线，同时巴尔末减幅显著增大。这些发射特征呈现出宽翼，其速度与星云阶段之前显著的P-Cygni轮廓推导的外流速度一致，因此被解释为源于之前抛出的 ejecta（抛射物），在X射线辐射减弱时膨胀并复合产生。本研究使用光电离代码Cloudy对该阶段进行建模，对电离连续谱和发射气体采用简单假设，定量再现了巴尔末减幅、Hα等效宽度等关键可观测值，定性再现了观测到的光谱。模拟显示，在氢密度n_H约10^10.5-10^12.5 cm^-3、电离参数logξ在-1.5≤logξ≤1范围内的数量级变化中，巴尔末减幅在观测范围内大致保持稳定，这支持了星云阶段可在抛射物适度膨胀和冷却中持续的场景，与观测结果一致。最后，本研究用不同方法约束星云阶段的一般属性，提出星云阶段由团块状、部分电离的抛射物产生，其总质量可能超过爆发期间的吸积质量。
英文摘要
Some of the most extreme galactic black hole transients exhibit a nebular phase at the end of their outbursts. This stage was first identified in the 2015 outburst of V404 Cygni, when it dominated the optical spectrum for ~4 days. It is characterised by exceptionally strong optical emission lines, together with a significant increase in the Balmer decrement. The emission features show broad wings reaching velocities consistent with outflow speeds derived from prominent P-Cygni profiles that preceded the nebular phase. They are thus interpreted as arising from previously launched ejecta that expand and recombine as X-ray irradiation declines. In this work, we modelled this phase using the photoionisation code Cloudy. Adopting simple assumptions for the irradiating continuum and emitting gas, we quantitatively reproduced key observables, such as the Balmer decrement and the H$α$ equivalent width, and qualitatively reproduced the observed spectra. Our simulations show that the Balmer decrement remains roughly stable within the observed range across orders-of-magnitude changes in the density and ionisation parameter, spanning $n_\mathrm{H} \sim 10^{10.5}-10^{12.5}\,\text{cm}^{-3}$ and $-1.5 \lesssim \logξ\lesssim 1$. This supports the scenario in which the nebular phase can persist through moderate ejecta expansion and cooling, consistent with observations. Finally, we used different approaches to constrain the general properties of the nebular phase, which we propose is produced by clumpy, partially ionised ejecta whose total mass likely exceeds the mass accreted during the outburst.
CommentsAccepted for publication in A&A
