时间：7月17日（周三）10：30

　　地点：多学科大楼416

　　报告人：黄晓渊博士 （紫金山天文台）

　　主持人：毕效军 研究员

　　题目：The Crab Nebula, a Self-organized Criticality System?

　　摘要：

　　Several analyses of the Crab Nebula have shown the flux of the low-energy component of the Crab Nebula from synchrotron radiation,

　　in some short time windows, could be significantly enhanced compared to the average value. In this paper, we investigate the Crab Nebula with

　　data in about ten years observation of the Fermi-LAT, and we identify 15 significant flares in the gamma-ray light curve of the low-energy component

　　with 4 days time bin. We confirm these significant flares could be decomposed into a steady synchrotron component, and an involving flare component

　　with a hard spectral index, about 1.53. We also find an almost linear correlation between the cutoff energy and the energy flux above 100 MeV of the

　　flare component for each significant outburst. We further decompose the gamma-ray light curve into the quiescent synchrotron and flare components

　　using a statistical method suitable for the self-organized criticality model. We find the flux of the synchrotron background is consistent with the value

　　derived from the composite likelihood analysis for significant flares,and a fluence distribution power-law index is about 1.75, which is consistent with

　　the theoretical prediction of the self-organized criticality system with the spatial dimension S = 3 and indicates that the gamma-ray flares of the Crab

　　Nebula are possibly driven by the same physical mechanism as that of the solar flares, i.e., magnetic reconnection.