标题： 钱德拉对两个星系团周围未分辨X射线源的观测 显示英文标题

标题： Chandra Observations of Unresolved X-ray Sources around two Clusters of Galaxies

摘要： 我们使用钱德拉X射线天文台，在两个丰富的星系团附近搜索未解析的X射线源：Abell 1995（A1995）和MS 0451.6-0305（MS0451）。 我们在A1995周围检测到的未解析源数量明显多于根据在深空\CHANDRA 观测中同一光度极限下检测到的X射线源数量所预期的数量。 以前的研究也利用\ROSAT $ $在几个附近星系团附近发现了过量的X射线源，并且最近利用钱德拉在更遥远（$z ~ 0.5$）的星系团（RXJ0030和3C295）中也发现了类似的过量X射线源。 相比之下，我们在MS0451附近仅检测到14个未解析的X射线源，这与无星系团背景预期的数量一致。 我们假设这些额外源位于其各自星系团的距离上，确定了这些额外源的光度函数。 A1995周围额外源的特征光度必须比RXJ0030和3C295周围额外源的特征光度暗一个数量级。 MS0451周围额外源的明显缺乏与它的更远距离以及与A1995源相同的特征光度是一致的。 硬度比表明，平均而言，A1995中的额外源可能比RXJ0030和3C295中的额外源具有更硬的光谱。 这些结果表明，不同类别的天体可能在不同的星系团中占主导地位，这可能取决于伴随星系团的形成历史和/或动力状态。 显示英文摘要

摘要： We have searched for unresolved X-ray sources in the vicinity of two rich clusters of galaxies: Abell 1995 (A1995) and MS 0451.6-0305 (MS0451), using the Chandra X-ray observatory. We detected significantly more unresolved sources around A1995 than expected based on the number of X-ray sources to the same flux limit detected in deep \CHANDRA observations of blank fields. Previous studies have also found excess X-ray sources in the vicinity of several nearby clusters of galaxies using \ROSAT$ $, and recently in more distant ($z ~ 0.5$) clusters (RXJ0030 and 3C295) using Chandra. In contrast, we detect only 14 unresolved X-ray sources near MS0451, which is consistent with the number expected from a cluster-free background. We determine the luminosity functions of the extra sources under the assumption that they are at the distance of their respective clusters. The characteristic luminosity of the extra sources around A1995 must be an order of magnitude fainter than that of the extra sources around RXJ0030 and 3C295. The apparent lack of extra sources around MS0451 is consistent with its greater distance and the same characteristic luminosity as the A1995 sources. Hardness ratios suggest that, on average, the extra sources in A1995 may have harder spectra than those of RXJ0030 and 3C295. These results indicate that different classes of objects may dominate in different clusters, perhaps depending on the formation history and/or dynamical state of the accompanying cluster.