Dip in UHECR and Transition from Galactic to Extragalactic Cosmic Rays

Abstract

The dip is a feature in the diffuse spectrum of UHE protons in energy range $1\times 10^{18}-4\times 10^{19}$ eV, which is caused by electron-positron pair production on CMB photons. Calculated for power-law generation spectrum with index ${\gamma }_g=2.7$, the shape of the dip is confirmed with high accuracy by data of Akeno - AGASA, HiRes, Yakutsk and Fly's Eye detectors. The predicted shape of the dip is robust: it is valid for the rectilinear and diffusive propagation, for different discretenesses in the source distribution, for local source overdensity and deficit, for source inhomogeneities on scale $\ell \lsim 100$ Mpc etc. Below the characteristic energy $E_c\approx 1\times 10^{18}$ eV the spectrum of the dip flattens for both diffusive and rectilinear propagation, and more steep galactic spectrum becomes dominant at $E<E_c$. The energy of transition $E_{\mathrm{tr}}<E_c$ approximately coincides with the position of the second knee $E_{2kn}$ observed in the cosmic ray spectrum. The critical energy $E_c$ is determined by the energy $E_{\mathrm{eq}}=2.3\times 10^{18}$ eV, where adiabatic and pair-production energy losses are equal. Thus, position of the second knee is explained by proton energy losses on CMB photons.

12 pages, 9 figures, new section is added, a technical problem is fixed

References in corpus (4)

• Dip in UHECR spectrum as signature of proton interaction with CMB
• Extra-galactic magnetic fields and the second knee in the cosmic-ray spectrum
• Anti-GZK effect in Ultra High Energy Cosmic Rays diffusive propagation
• The mass composition of cosmic rays above 10^17 eV

Cited by in corpus (3)

• The Cosmic-Ray Energy Spectrum between 2 PeV and 2 EeV Observed with the TALE detector in monocular mode
• Cosmic-ray composition and its relation to shock acceleration by supernova remnants
• Cosmic Rays above the Knee