标题： XMM-Newton看到的超亮X射线源的种群 显示英文标题

标题： The population of hyperluminous X-ray sources as seen by XMM-Newton

摘要： 超亮和极高亮度X射线源（ULXs和HLXs）是X射线天空中最明亮的天体之一。 虽然ULXs很可能包含以超爱丁顿率吸积的恒星级致密天体，但HLXs则是吸积中等质量黑洞的有力候选者。 我们的目标是通过去除可能的污染物来生成一个干净的HLX样本，并表征剩余群体的光谱特性。 从XMM-Newton检测到的115个HLX开始，我们识别并去除了污染物（AGNs，被检测为点源的X射线弥散辐射，以及潮汐撕裂事件候选者），并获得了40个XMM-Newton光谱可用的源。 我们用吸收幂律模型拟合它们，并确定了它们的未吸收光度和硬度比。 我们构建了硬度-光度图，将结果与HLX原型ESO 243-49 HLX-1的光谱特性进行了比较，并对几个有希望的候选者进行了更深入的分析。 结果表明，HLX群体的光度范围从$1\times10^{41}$ erg s$^{-1}$到几乎$10^{43}$ erg s$^{-1}$，并在硬度0.5到5之间均匀分布。 一半的人口硬度比典型AGN高，可以被认为是ULX人群在更高能量下的延伸。 我们发现了四个非常柔软的异常值，它们的特点是陡峭的幂律光谱，在1$-$2 keV以上的X射线发射没有，类似于ESO 243-49 HLX-1。 那些具有多历元档案数据的源显示出光度变化高达几乎两个数量级。 我们表明，目前被识别为HLX的源可能比ULX更多样化，利用现有数据区分不同类型的物体并不容易。 新的观测将有助于扩大当前样本并揭示这一类许多物体的真实性质。 显示英文摘要

摘要： Ultraluminous and hyperluminous X-ray sources (ULXs and HLXs) are among the brightest astrophysical objects in the X-ray sky. While ULXs most likely host stellar-mass compact objects accreting at super-Eddington rates, HLXs are compelling candidates for accreting intermediate-mass black holes. Our goal is to produce a clean sample of HLXs by removing possible contaminants and characterise the spectral properties of the remaining population. Starting with a set of 115 HLXs detected by XMM-Newton, we identified and removed contaminants (AGNs, X-ray diffuse emission detected as point-like, and tidal disruption event candidates) and retrieved 40 sources for which XMM-Newton spectra are available. We fitted them with an absorbed power law model and determined their unabsorbed luminosities and hardness ratios. We constructed the hardness-luminosity diagram, compared the results with the spectral properties of the HLX prototype, ESO 243-49 HLX-1, and conducted a deeper analysis on a few promising candidates. The resulting HLX population spans a luminosity range from $1\times10^{41}$ erg s$^{-1}$ to nearly $10^{43}$ erg s$^{-1}$ and is homogeneously spread in hardness between 0.5 and 5. Half of the population has hardness ratios higher than a typical AGN, and could be considered the extension of the ULX population at higher energies. We found four very soft outliers, which are characterised by steep power law spectra and no X-ray emission above 1$-$2 keV, similarly to ESO 243-49 HLX-1. Those with multi-epoch archival data show changes in luminosity up to almost two orders of magnitudes. We show that sources currently identified as HLXs can be more diverse than ULXs and disentangling between different types of objects is not trivial with currently available data. New observations would be beneficial to expand the current sample and uncover the true nature of many objects of this class.