Misc,
Relativistic Reconnection: an Efficient Source of Non-Thermal Particles
(Jan 21, 2014)
Abstract
In magnetized astrophysical outflows, the dissipation of field energy into
particle energy via magnetic reconnection is often invoked to explain the
observed non-thermal signatures. By means of two- and three-dimensional
particle-in-cell simulations, we investigate anti-parallel reconnection in
magnetically-dominated electron-positron plasmas. Our simulations extend to
unprecedentedly long temporal and spatial scales, so we can capture the
asymptotic state of the system beyond the initial transients, and without any
artificial limitation by the boundary conditions. At late times, the
reconnection layer is organized into a chain of large magnetic islands
connected by thin X-lines. The plasmoid instability further fragments each
X-line into a series of smaller islands, separated by X-points. At the
X-points, the particles become unmagnetized and they get accelerated along the
reconnection electric field. We provide definitive evidence that the late-time
particle spectrum integrated over the whole reconnection region is a power-law,
whose slope is harder than -2 for magnetizations sigma>10. Efficient particle
acceleration to non-thermal energies is a generic by-product of the long-term
evolution of relativistic reconnection in both two and three dimensions. In
three dimensions, the drift-kink mode corrugates the reconnection layer at
early times, but the long-term evolution is controlled by the plasmoid
instability, that facilitates efficient particle acceleration, in analogy to
the two-dimensional physics. Our findings have important implications for the
generation of hard photon spectra in pulsar winds and relativistic
astrophysical jets.
