时间：2014年5月16日上午9:30
地点：行政科研楼1514
报告人：Greg Werner
单位：美国科罗拉多大学

摘要：Magnetic reconnection transforms magnetic field energy into particle kinetic energy; it may be the mechanism for accelerating particles to high enough energies to emit energetic synchrotron radiation, which is observed in various astrophysical objects, including pulsars, active Galactic nuclei, and gamma-ray bursts. Using 2D particle-in-cell simulations of relativistic, radiating, pair plasma reconnection, this work demonstrates that reconnection accelerates particles, bunching and focusing the most energetic particles into a narrow beam that wiggles in the plane of the reconnection layer. This beaming leads to brief, intense flares of high-energy photons when the beam crosses the line of sight. A newly-developed PIC code, which includes the radiation reaction, has recently shed new light (so to speak) on the picture of relativistic reconnection under strong synchrotron cooling. The most energetic particles feel very little radiative losses while they are accelerated in a straight line deep inside the layer where the electric field exceeds the magnetic field.
Eventually, the particles get kicked out of the layer and subsequently radiate >160 MeV synchrotron radiation, which would be impossible to explain with ideal MHD-based models of particle acceleration. This result is essential in understanding the origin of >100 MeV gamma-ray flares observed in the Crab Nebula.