标题： OGLE对大麦云微透镜效应的观测。 III. 利用OGLE-III LMC数据排除亚太阳质量的MACHOs 显示英文标题

标题： The OGLE View of Microlensing towards the Magellanic Clouds. III. Ruling out sub-solar MACHOs with the OGLE-III LMC data

摘要： 在呈现光学引力透镜实验（OGLE）对暗物质晕致密天体（MACHOs）微透镜研究的系列文章的第三部分中，我们描述了OGLE-III对大麦哲伦星云（LMC）的监测结果。 这个前所未有的数据集包含了大约3500万个分布在40平方度区域内的天体，在8年的时间里几乎连续的光度覆盖。 我们报告了通过自动管道检测到的两个候选微透镜事件，以及另外两个概率较低的候选事件，这些事件是手动发现的。 对于这两个主要候选事件，我们通过详细的混合检查和检测效率确定计算出了光学深度，结果为 tau=(0.16±0.12)10^-7。 如果我们在观测中发现的微透镜信号源自MACHOs，这意味着它们的质量约为0.2 M_Sun，并且它们仅占银河晕质量的f=3±2%。 然而，我们的检测更可能的解释完全不涉及暗物质致密天体，而是依赖于LMC恒星由LMC透镜引起的自透镜自然效应。 在这种情况下，我们可以几乎完全排除亚太阳质量范围内的MACHOs，其上限为f<7%，在M=0.1 M_Sun时达到最小值f<4%。 对于质量接近M=10 M_Sun的MACHOs，限制则较为宽松，f约为20%。 由于调查的局限性，没有为更重的质量找到合理的限制，只剩下极小的质量谱范围仍可用于暗物质致密天体。 显示英文摘要

摘要： In the third part of the series presenting the Optical Gravitational Lensing Experiment (OGLE) microlensing studies of the dark matter halo compact objects (MACHOs) we describe results of the OGLE-III monitoring of the Large Magellanic Cloud (LMC). This unprecedented data set contains almost continuous photometric coverage over 8 years of about 35 million objects spread over 40 square degrees. We report a detection of two candidate microlensing events found with the automated pipeline and an additional two, less probable, candidate events found manually. The optical depth derived for the two main candidates was calculated following a detailed blending examination and detection efficiency determination and was found to be tau=(0.16+-0.12)10^-7. If the microlensing signal we observe originates from MACHOs it means their masses are around 0.2 M_Sun and they compose only f=3+-2 per cent of the mass of the Galactic Halo. However, the more likely explanation of our detections does not involve dark matter compact objects at all and rely on natural effect of self-lensing of LMC stars by LMC lenses. In such a scenario we can almost completely rule out MACHOs in the sub-solar mass range with an upper limit at f<7 per cent reaching its minimum of f<4 per cent at M=0.1 M_Sun. For masses around M=10 M_Sun the constraints on the MACHOs are more lenient with f ~ 20 per cent. Owing to limitations of the survey there is no reasonable limit found for heavier masses, leaving only a tiny window of mass spectrum still available for dark matter compact objects.