ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES AND LARGE-SCALE MAGNETIC-FIELDS

Protons of energies up to about 10(20) eV can be subject to significan t deflection and energy-dependent time delay in large-scale extragalac tic or halo magnetic fields of strengths comparable to current upper l imits. By performing three-dimensional Monte Carlo simulations of nucl eon propagation, we show how observations of arrival direction and tim e distributions can be used to measure the structure and strength of l arge-scale magnetic fields and constrain the nature of the source of u ltra-high-energy cosmic rays.