Multiple UHECR Events from Galactic hadron jets

We propose a new observational test of top-down source models for the ultra-high-energy cosmic-rays (UHECRs), based on the simultaneous observation of two or more photons from the same Galactic hadron jet. We derive a general formula allowing one to calculate the probability of detecting such `multiple events', for any particular top-down model, once the physical parameters of the associated hadron jets are known. We then apply our results to a generic top-down model involving the decay of a supermassive particle, and show that under reasonable assumptions the next-generation UHECR detectors would be able to detect multiple events on a timescale of a few years, depending on the mass of the top-down progenitor. Either the observation or the non-observation of such events will provide constraints on the UHECR top-down models and/or the physics of hadronization at ultra-high energy.Comment: 14 pages + 1 appendix, 3 figures, accepted for publication in Astroparticle Physic

Photodisintegration of Ultra-High-Energy Cosmic Rays revisited

Recent microscopic and phenomenological calculations of giant dipole resonances for A <= 56 nuclei are presented. The derived photodisintegration cross sections are exhaustively compared to the photonuclear data available to date. An accurate description of the data is found. Our new calculations are also compared with the previous and widely-used estimates of Puget, Stecker and Bredekamp. The present calculations also include all the possible paths down the nuclear chart. The impact on the photodisintegration of ultra-high-energy cosmic rays (UHECR) is illustrated for a Fe source with typical energies of 10^{20-21} eV. At energies around 10^20 eV, the new cross sections are found to modify the UHECR photodisintegration rates. At energies around 10^21 eV, it is recommended to solve a full reaction network to estimate the photodisintegration rate of the UHECR.Comment: 16 pages, 8 figures, accepted for publication in Astroparticle Physic