Time Structure of Ultra-High Energy Cosmic Ray Sources and Consequences for Multi-messenger Signatures
Abstract
The latest results on the sky distribution of ultra-high energy cosmic ray sources have consequences for their nature and time structure. If the sources accelerate predominantly nuclei of atomic number A and charge Z and emit continuously, their luminosity in cosmic rays above ~6x1019 eV can be no more than a fraction of ~5x10-4 Z-2 of their total power output. Such sources could produce a diffuse neutrino flux that gives rise to several events per year in neutrino telescopes of km3 size. Continuously emitting sources should be easily visible in photons below ~100 GeV, but not in TeV gamma-rays which are likely absorbed within the source. For episodic sources that are beamed by a Lorentz factor Gamma, the bursts or flares have to last at least ~0.1 Gamma-4 A-4 yr. A considerable fraction of the flare luminosity could go into highest energy cosmic rays, in which case the rate of flares per source has to be less than ~5x10-3 Gamma4 A4 Z2 yr-1. Episodic sources should have detectable variability both at GLAST and TeV energies, but neutrino fluxes may be hard to detect.