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Cosmic Magnetic Lenses

Magnetic fields play a critical role in the propagation of charged cosmic rays. Particular field configurations supported by different astrophysical objects may be observable in cosmic ray maps. We consider a simple configuration, a constant azimuthal field in a disk-like object, that we identify as a cosmic magnetic lens. Such configuration is typical in most spiral galaxies, and we assume that it can also appear at smaller or larger scales. We show that the magnetic lens deflects cosmic rays in a regular geometrical pattern, very much like a gravitational lens deflects light but with some interesting differences. In particular, the lens acts effectively only in a definite region of the cosmic-ray spectrum, and it can be convergent or divergent depending on the (clockwise or counterclockwise) direction of the magnetic field and the (positive or negative) electric charge of the cosmic ray. We find that the image of a point-like monochromatic source may be one, two or four points depending on the relative position of source, observer and center of the lens. For a perfect alignment and a lens in the orthogonal plane the image becomes a ring. We also show that the presence of a lens c