Supersoft X-rays sources (SSSs) have been proposed as potential Type Ia supernova (SN Ia) progenitors. If such objects are indeed persistently X-ray luminous and embedded in sufficiently dense ISM, they will be surrounded by extended nebular emission. These nebulae should persist even long after a SN Ia explosion, due to the long recombination and cooling times involved. With this in mind, we searched for nebular [O III] emission around four SSSs and three SNRs in the Large Magellanic Cloud, using the 6.5m Baade telescope at Las Campanas Observatory and the IMACS camera. We confirm that, out of the four SSS candidates, only CAL 83 can be associated with an [O III] nebula. The [O III] luminosity for the other objects are constrained to $\lesssim 17\%$ of that of CAL 83 at 6.8 pc from the central source. Models computed with the photoionization code CLOUDY indicate that either the ISM densities in the environments of CAL 87, RX J0550.0-7151 and RX J0513.9-6951 must be significantly lower than surrounding CAL 83, or the average X-ray luminosities of these sources over the last $\lesssim 10,000$ years must be significantly lower than presently observed, in order to be consistent with the observed luminosity upper limits. For the three SNRs we consider (all with ages $< 1000$ years), our [O III] flux measurements together with the known surrounding ISM densities strongly constrain the ionizing luminosity of their progenitors in the last several thousand years, independent of the progenitor channel.

中文翻译：

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大麦哲伦云中的超软 X 射线星云

超软 X 射线源 (SSS) 已被提议作为潜在的 Ia 型超新星 (SN Ia) 前身。如果这些天体确实持续发光并嵌入足够密集的 ISM 中，它们将被扩展的星云辐射包围。由于涉及较长的重组和冷却时间，这些星云甚至在 SN Ia 爆炸后仍会持续很长时间。考虑到这一点，我们使用拉斯坎帕纳斯天文台的 6.5m 巴德望远镜和 IMACS 相机搜索了大麦哲伦云中四个 SSS 和三个 SNR 周围的星云 [O III] 发射。我们确认，在四个 SSS 候选星云中，只有 CAL 83 可以与 [O III] 星云相关联。其他天体的 [O III] 光度被限制为 CAL 83 在距离中心光源 6.8 pc 处的光度的 $\lesssim 17\%$。使用光电离代码 CLOUDY 计算的模型表明，CAL 87、RX J0550.0-7151 和 RX J0513.9-6951 环境中的 ISM 密度必须显着低于周围的 CAL 83，或者过去 $\lesssim 10,000$ 年的这些来源必须明显低于目前观察到的，以便与观察到的光度上限保持一致。对于我们考虑的三个 SNR（年龄均小于 1000 年），我们的 [O III] 通量测量以及已知的周围 ISM 密度在过去几千年中强烈限制了其祖先的电离光度，与祖先无关渠道。9-6951 必须明显低于周围的 CAL 83，或者这些源在过去 $\lesssim 10,000$ 年的平均 X 射线光度必须明显低于目前观察到的，以便与观察到的光度上限一致. 对于我们考虑的三个 SNR（年龄均小于 1000 年），我们的 [O III] 通量测量以及已知的周围 ISM 密度在过去几千年中强烈限制了其祖先的电离光度，与祖先无关渠道。9-6951 必须明显低于周围的 CAL 83，或者这些源在过去 $\lesssim 10,000$ 年的平均 X 射线光度必须明显低于目前观察到的，以便与观察到的光度上限一致. 对于我们考虑的三个 SNR（年龄均小于 1000 年），我们的 [O III] 通量测量以及已知的周围 ISM 密度在过去几千年中强烈限制了其祖先的电离光度，与祖先无关渠道。