Search

Both the acceleration of cosmic rays (CR) in supernova remnant shocks and their subsequent propagation through the random magnetic field of the Galaxy are deemed to result in an almost isotropic CR spectrum. Yet the MILAGRO TeV observatory and the IceCube discovered sharp (~ 10°) arrival anisotropies of CR nuclei. We suggest a mechanism for producing such a CR beam which operates en route to the observer. The key assumption is that CRs are scattered by a strongly anisotropic Alfven wave spectrum formed by the turbulent cascade across the local field direction. The strongest pitch-angle scattering occurs for particles moving almost precisely along the field line. Partly because this direction is also the direction of minimum of the large scale CR angular distribution, the enhanced scattering results in a weak but narrow particle excess. The width, the fractional excess and the maximum momentum of the beam are calculated from a systematic transport theory depending on a single scale l which can be associated with the longest Alfven wave, efficiently scattering the beam. The best match to all the three characteristics of the beam is achieved at l ~ 1pc. The distance to a possible source of the beam is estimated to be within a few 100pc. Possible approaches to determination of the scale l from the characteristics of the source are discussed. The beam related large scale anisotropic CR component is found to be energy independent which is also consistent with the observations. The beam splitting mechanism to explain the combined Milagro and IceCube observations is suggested. [ABSTRACT FROM AUTHOR]

Cosmic ray protons accelerated in strong shocks are known to drive various instabilities in the shock precursor. An acoustic instability of the shock precursor driven by the pressure gradient of accelerated particles is studied in the nonlinear regime. After nonlinear steepening of the unstable waves an ensemble of discontinuities, a shocktrain, is created. Traveling wave solutions are obtained analytically and verified dynamically by numerical calculations. By compressing both an ambient and turbulent magnetic fields, and by generating the flow vorticity, the shocktrains not only amplify the magnetic field but also form distinct magnetic structures. These structures change the transport regime of accelerated particles from diffusive (quasi-linear regime) at lower momenta to fractionally kinetic (Levy flights and traps) over an extended momentum interval below the spectrum cut-off. As a result, a spectral break should form, typically at sub-Tev energies and some of the particles of higher energies escape upstream before they reach the cut-off momentum. [ABSTRACT FROM AUTHOR]