标题： 一个解释蟹状星云伽马射线变化和耀斑的统计模型 显示英文标题

标题： A statistical model to explain the gamma-ray variability and flares of the Crab nebula

摘要： 最近，AGILE和Fermi/LAT探测器从蟹状星云中发现了巨大的$\gamma$射线爆发。这些爆发的持续时间是几天。Fermi/LAT数据按月时间分箱进一步显示了同步辐射尾部的显著变化，而逆康普顿成分是稳定的。在X射线、光学、红外和射电波段的同时或后续观测中没有发现明显的通量变化。基于这些观测，我们提出$\gamma$射线的变化和爆发是由于可以将电子加速到$\sim$PeV能量的结的统计波动所致。电子的最大可达到的能量被假定与结的大小成正比，该结的大小被假设遵循幂律分布。因此，由于小结的数量众多，低能电子通量将保持稳定，而高能电子通量可能会经历大的波动。这种情形的蒙特卡洛实现可以在适当模型参数的情况下很好地再现观测数据。 显示英文摘要

摘要： Recently the AGILE and Fermi/LAT detectors uncovered giant $\gamma$-ray flares from the Crab nebula. The duration of these flares is a few days. The Fermi/LAT data with monthly time binning further showed significant variability of the synchrotron tail of the emission, while the inverse Compton component was stable. The simultaneous or follow-up observations in X-ray, optical, infrared and radio bands did not find significant flux variation. Based on these observations, we propose that the $\gamma$-ray variability and flares are due to statistical fluctuations of knots that can accelerate electrons to $\sim$PeV energies. The maximum achievable energy of electrons is adopted to be proportional to the size of the knot, which is assumed to follow a power-law distribution. Thus the low energy electron flux will be stable due to the large number of small knots, while the high energy electron flux may experience large fluctuations. Monte Carlo realization of such a picture can reproduce the observational data quite well given proper model parameters.