基于LHAASO实验研究蟹状星云耀发机制

The Crab Nebula is well known as a standard candle, which is a steady radiation source, however the gamma ray flares from the Crab Nebula have been observed many times by AGILE and Fermi-LAT since 2007 and lasted several days each time. The strongest emission, observed during the 2011 April “superflare”, exceeded the quiescent level by more than several times. These observations challenge the standard models for particle acceleration in pulsar wind nebulae, and the reason has not been explained completely. Due to the limitation of observation condition, current main detectors have not observed gamma ray above 100 TeV from the Crab Nebula. Searching for ultra-high energy gamma ray sources is one of the most significant physics goals in Large High Altitude Air Shower Observatory (LHAASO) experiment, LHAASO can observe the gamma ray from the Crab Nebula above 100 TeV with very high sensitivity. These observations will greatly improve to understand the structure and evolution of pulsar wind nebulae. We construct an effective and robust discrimination parameter to reject the hadronic background, and deeply check by both simulation and experiment data, which will greatly improve the sensitivity of searching for ultra-high energy gamma ray sources. The study will also be well referenced by many other cosmic ray experiments.

蟹状星云被视为“标准烛光”，属于稳定的辐射源，然而自2007年以来被AGILE和Fermi-LAT多次观测到能够持续几天之久的耀发现象，更为甚者的是2011年4月的巨型耀发，超过平静期流强的数倍。这些观测现象对脉冲星风云的经典粒子加速机制提出了挑战，成因尚未完全弄清楚。目前主流伽马探测器由于自身观测条件限制，在百TeV伽马射线辐射至今尚未曾探测到。我国正在建设的高海拔宇宙线观测站的主要物理目标之一是寻找超高能伽马射线源，其在百TeV能段上对蟹状星云观测具有极高的灵敏度，将填补蟹状星云在百TeV能段上的观测空白，观测结果将对理解脉冲星风云的结构、演化等基础问题产生重大促进作用。本项目发展出的伽马质子鉴别方法也将为相关的伽马天文物理研究奠定良好的基础，鉴别方法也将在国际其他宇宙线实验中有很好的借鉴作用。

蟹状星云是天文领域内众多实验观测研究的热点源，其伽马射线辐射测量在近十年取得了多项重要进展。本项目基于高海拔宇宙线观测站的一平方公理阵列（KM2A）的实验数据和宇宙线模拟样本，全面研究了KM2A探测器各项性能，开发了一套完整的伽马天文物理的分析程序；测量分析了蟹状星云能谱，首次发现来自蟹状星云方向的PeV光子，使用单区理论模型拟合能谱发现高能段上有4倍标准偏差的差异，表明在现有的理论模型上蟹状星云的高能辐射还存在着未解之谜，还需要累积更多的实验数据进一步探索和发现；搜寻了蟹状星云100TeV能量段以上的耀发现象，截至目前未发现有耀发现象，在MeV-GeV能段上，Fermi卫星同时期也未探测到蟹状星云的耀发。