Gamma-ray bursters as sources of cosmic rays

The little we do know of the physical conditions in gamma-ray bursters makes them conducive to the acceleration of high-energy cosmic rays, especially if they are at cosmological distances. We find that, with the observed statistics and fluxes of gamma-ray bursts, cosmological bursters may be an important source of cosmic rays in two regions of the observed spectrum: 1. At the very-high-energy end (E>10^{19} eV), where cosmic rays must be of extragalactic origin. 2. Around and above the spectral feature that has been described as a bump and/or a knee, which occurs around 10^{15} eV, and starts at about 10^{14} eV. The occasional bursters that occur inside the Galaxy--about once in a few hundred thousand years if burst emission is isotropic; more often, if it is beamed--could maintain the density of galactic cosmic rays at the observed level in this range. These two energy ranges might correspond to two typical energy scales expected from bursters: one pertinent to acceleration due to interaction of a magnetized-fireball front with an ambient medium; the other to acceleration in the fireball itself (e.g. shock acceleration).Comment: 12 pages in Late

Stability of magnetic vortex in soft magnetic nano-sized circular cylinder

Stability of magnetic vortex with respect to displacement of its center in a nano-scale circular cylinder made of soft ferromagnetic material is studied theoretically. The mode of vortex displacement producing no magnetic charges on the cylinder side is proposed and the corresponding absolute single-domain radius of the cylinder is calculated as a function of its thickness and the exchange length of the material. In cylinders with the radii less than the single-domain radius the vortex state is unstable and is absolutely prohibited (except if pinned by material imperfections), so that the distribution of the magnetization vector in such cylinders in no applied magnetic field is uniform (or quasi-uniform). The phase diagram of nano-scale cylinders including the stability line and the metastability region obtained here is presented.Comment: 3 pages, 2 figures, RevTex 4, presented at JEMS'01, accepted to JMM

Transition radiation in the quantum regime as a diffractive phenomenon

We demonstrate that the transition photon radiation and pair creation can be interpreted as a diffractive phenomenon in terms of the light-cone wave functions in a way similar to the Good-Walker approach [6] to the diffraction dissociation. Our formulas for spectra agree with those obtained by Baier and Katkov [5] within the quasiclassical operator method. However, there is some disagreement with earlier results by Garibyan [4].Comment: 7 pages. The journal version published in Phys. Lett.