M_（51）两个超亮X射线源的多波段对应
Multiband counterparts of two eclipsing ultraluminous X-ray sources in M 51
摘要：
我们提出的发现和解释的电离星云周围的两个超明亮的X射线源在M 51;这两个源共享的罕见的属性，显示X射线日食的伴星，因此是后续研究的主要目标。利用哈勃太空望远镜的存档图像，我们发现了一个与一个X射线源（CXOM 51 J132940.0+471237; ULX-1为简单起见）相关的拉长的100 pc长的发射线结构，以及在第二个源（CXOM 51 J132939.5+471244; ULX-2为简单起见）位置的一个更圆形的电离星云。我们用大型双筒望远镜的多目标双光谱仪观测了这两个星云。从我们的光谱分析，我们认为，在ULX-1气泡中的气体是冲击电离的，与一个喷流的动力学功率的$\approx$ 2 $\times 10^{39}$ erg s $^{-1}$的效果一致。也可能存在额外的X射线光电离，以解释高电离线的强度，例如He II $λ4686$和[Ne V] $λ3426$。另一方面，ULX-2气泡的发射线是正常O型星光电离的典型特征，这表明该星云实际上是一个H II区域，与ULX没有物理关系，而只是一个偶然的排列。从存档的甚大阵列数据中，我们还在ULX-1气泡的位置（与其喷射源一致）检测到空间扩展，陡谱无线电发射，但没有ULX-2的无线电对应物（与该源周围缺乏冲击电离气体一致）。
英文摘要：
We present the discovery and interpretation of ionized nebulae around two ultraluminous X-ray sources in M 51; both sources share the rare property of showing X-ray eclipses by their companion stars, and are therefore prime targets for follow-up studies. Using archival Hubble Space Telescope images, we found an elongated, 100-pc-long emission-line structure associated with one X-ray source (CXOM51 J132940.0+471237; ULX-1 for simplicity), and a more circular, ionized nebula at the location of the second source (CXOM51 J132939.5+471244; ULX-2 for simplicity). We observed both nebulae with the Large Binocular Telescope's Multi-Object Double Spectrograph. From our analysis of the optical spectra, we argue that the gas in the ULX-1 bubble is shock-ionized, consistent with the effect of a jet with a kinetic power of $\approx$2 $\times 10^{39}$ erg s$^{-1}$. Additional X-ray photo-ionization may also be present, to explain the strength of high-ionization lines such as He II $λ4686$ and [Ne V] $λ3426$. On the other hand, the emission lines from the ULX-2 bubble are typical for photoionization by normal O stars suggesting that the nebula is actually an H II region not physically related to the ULX but is simply a chance alignment. From archival Very Large Array data, we also detect spatially extended, steep-spectrum radio emission at the location of the ULX-1 bubble (consistent with its jet origin), but no radio counterpart for ULX-2 (consistent with the lack of shock-ionized gas around that source).
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