An almost perfect round hole of CO-line emission with a diameter of 3.7 pc was found in a molecular cloud (MC) centered on G35.75-0.25 ($l = 35^\circ.75, b = -0^\circ.25$) at radial velocity of 28 km s$^{-1}$. The hole is quiet in radio continuum emission, unlike the usual supernova remnants (SNR), and the molecular edge is only weakly visible in 8 and 24 $\mu$m dust emissions. The hole may be either a fully evolved molecular bubble around a young stellar object (YSO), or a relic of a radio-quiet SNR that has already stopped expansion after rapid evolution in the dense MC as a buried SNR. Because G35.75 exhibits quite different properties from YSO-driven bubbles of the same size, we prefer the latter interpretation. Existence of such a "dark" SNR would affect the estimation of the supernova rate, and therefore the star formation history in the Galaxy.

中文翻译：

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暗超新星遗迹

在以 G35.75-0.25 ($l = 35^\circ.75, b = -0^\circ) 为中心的分子云 (MC) 中发现了一个直径为 3.7 pc 的几乎完美的 CO 线发射圆孔.25$) 径向速度为 28 公里 s$^{-1}$。与通常的超新星遗迹 (SNR) 不同，该洞在无线电连续谱发射中是安静的，并且分子边缘仅在 8 和 24 $\mu$m 尘埃发射中微弱可见。这个洞可能是一个围绕年轻恒星天体 (YSO) 的完全演化的分子气泡，或者是在密集的 MC 中快速演化后作为掩埋的 SNR 已经停止膨胀的无线电静默 SNR 的遗迹。因为 G35.75 表现出与 YSO 驱动的相同大小气泡完全不同的特性，我们更喜欢后一种解释。这种“暗”信噪比的存在会影响超新星率的估计，