Galactic Constraints on the Sources of Ultra-High Energy Cosmic Rays

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We show that if the sources of ultra-high energy cosmic rays (UHECRs) with energies E>10¹⁹eV are associated with galaxies, then the production of UHECRs must occur in transient events. Our galaxy is currently at a dim state in between transients. The time interval between transients is >3x10⁴ years if the minimum Lorentz factor to which protons are accelerated in the transients is between 10³ and 10⁷. This constraint is satisfied by gamma-ray bursts.