1205.3450 (V. Bosch-Ramon)

Fermi~I particle acceleration in converging flows mediated by magnetic reconnection    [PDF]

V. Bosch-Ramon

Converging flows with strong magnetic fields of different polarity can accelerate particles through magnetic reconnection. If the particle mean free path is larger than the thickness of the reconnection layer, but much smaller than the entire reconnection structure, the particle will mostly interact with the incoming flows potentially with a very low escape probability. We explore, in general and also in some specific scenarios, the possibility of particles being accelerated in a magnetic reconnection layer by interacting only with the incoming flows. We characterize converging flows undergoing magnetic reconnection, and derive analytical estimates for the particle energy distribution, acceleration rate, and maximum energies achievable in these flows. We also discuss a possible scenario, based on jets dominated by magnetic fields of changing polarity, in which this mechanism may operate. The proposed acceleration mechanism operates if the thickness of the reconnection layer is much smaller than its transversal characteristic size, and the magnetic field has a disordered component. Synchrotron losses may prevent electrons from entering in this acceleration regime. The acceleration rate should be faster, and the energy distribution of particles harder, than in standard diffusive shock acceleration. The interaction of obstacles with the innermost region of jets in active galactic nuclei and microquasars may be suitable sites for particle acceleration in converging flows.

View original: http://arxiv.org/abs/1205.3450