Maps of low-inclination nearby galaxies in Sloan Digitized Sky Survey u-g, g-r and r-i colors are used to determine whether Ultraluminous X-ray sources (ULXs) are predominantly associated with star-forming regions of their host galaxies. An empirical selection criterion is derived from colors of HII regions in M81 and M101 that differentiates between the young, blue stellar component and the older disk and bulge population. This criterion is applied to a sample of 58 galaxies of Hubble type S0 and later and verified through an application of Fisher's linear discriminant analysis. It is found that 60% (49%) of ULXs in optically-bright environments are within regions blueward of their host galaxy's HII regions compared to only 27% (0%) of a control sample according to the empirical (Fisher) criterion. This is an excess of 3-sigma above the 32% (27%) expected if the ULXs were randomly distributed within their galactic hosts. This indicates a ULX preference for young, approximately <10 Myr, OB associations. However, none of the ULX environments have the morphology and optical brightness suggestive of a massive young super star cluster though several are in extended or crowded star-forming (blue) environments that may contain clusters unresolved by Sloan imaging. Ten of the 12 ULX candidates with estimated X-ray luminosities in excess of 3e39 erg/s are equally divided among the group of ULX environments redward of HII regions and the group of optically faint regions. This likely indicates that the brightest ULXs turn on at a time somewhat later than typical of HII regions; say 10-20 Myr after star formation has ended. This would be consistent with the onset of an accretion phase as the donor star ascends the giant branch if the donor is a <20 solar-mass star.
The two Ultraluminous X-ray sources in the galaxy NGC 925
NGC 925 ULX-1和ULX-2是位于NGC 925中的两个超亮X射线源，距离为8.5 Mpc。这是我们第一次分析两个来源的高质量，同时XMM-Newton和NuSTAR数据。虽然乍一看ULX-1类似于一个中等质量的黑洞候选者（IMBH），因为它的高X射线光度（$(2$ $-$ $4)\times10^{40}$ erg s $^{-1}$）和它的光谱/时间的特点，仔细检查表明，它的属性更类似于一个典型的超爱丁顿吸积恒星黑洞，我们将其归类为一个“加宽的光盘”超明亮的X射线源。基于这种光谱状态的物理解释，我们建议，ULX-1被认为是在小倾角，可能通过一个强大的风起源于吸积盘疏散锥。ULX-2的光谱分类是不太确定的，但我们不赞成IMBH吸积亚爱丁顿率，因为它的光谱/时间属性可以关联到银河系吸积黑洞二进制的软或硬状态。
Spectroscopic Studies of an Ultraluminous Supersoft X-Ray Source in M81
超铝超软X射线源（Ultraluminous supersoft X-ray source，ULS）具有黑体温度低于0.1 keV，辐射热光度高于10 $^{39}$ ergs $^{-1}$的超软X射线谱。在这封信中，我们报告的第一个光学光谱观测的ULS在M81使用的LRIS光谱仪的凯克我望远镜。检测到的Balmer发射线显示出400 $\pm$ 80 km s $^{-1}$的平均内禀速度色散，这是一致的，从吸积盘。在蓝色一侧的连续谱的光谱指数也与多色盘模型一致。H $_α$发射线相对于当地恒星环境的速度为180 km s $\sim$，表明该ULS可能是M81中的一个古老星族晕系.在相隔四个晚上的两次观测之间，没有发现H $_α$发射线的显著变化。
The Redshift Evolution of Ultraluminous X-Ray Sources out to z~0.5: Comparison with X-Ray Binary Populations and Contribution to the Cosmic X-Ray Background
