A dip in the UHECR spectrum and the transition from galactic to extragalactic cosmic rays
By R. Aloisio, V. Berezinsky, P. Blasi, A. Gazizov, S. Grigorieva, B. Hnatyk. 2006
143 citations recorded by the source corpus.
Abstract The dip is a feature in the diffuse spectrum of ultra-high energy (UHE) protons in the energy range 1 × 10 18 –4 × 10 19 eV, which is caused by electron–positron pair production on the cosmic microwave background (CMB) radiation. For a power-law generation spectrum E −2.7 , the calculated position and shape of the dip is confirmed with high accuracy by the spectra observed by the Akeno-AGASA, HiRes, Yakutsk and Fly’s Eye detectors. When the particle energies, measured in these detectors, are calibrated by the dip, their fluxes agree with a remarkable accuracy. The predicted shape of the dip is quite robust: it is modified very weakly when the discreteness and inhomogeneities in the source distribution are taken into account, and for different regimes of propagation (from rectilinear to diffusive). The cosmological evolution of the sources, with parameters inspired by observations of Active Galactic Nuclei (AGN), also results in the same shape of the dip. The dip is modified strongly when the fraction of nuclei heavier than protons is high at injection, which imposes some restrictions on the mechanisms of acceleration operating in UHECR sources. The existence of the dip, confirmed by observations, implies that the transition from galactic to extragalactic cosmic rays occurs at E ≲ 1 × 10 18 eV. We show that at energies lower than a characteristic value E cr ≈ 1 × 10 18 eV, determined by the equality between the rate of energy losses due to pair production and adiabatic losses, the spectrum of extragalactic cosmic rays flattens in all cases of interest, and it provides a natural transition to a steeper galactic cosmic ray spectrum. This transition occurs at some energy below E cr , corresponding to the position of the so-called second knee. We discuss extensively the constraints on this model imposed by current knowledge of acceleration processes and sources of UHECR and compare it with the traditional model of transition at the ankle.
Subfields: Nuclear and High Energy Physics
View Paper: https://www.semanticscholar.org/paper/893aa6743675348163319ddcb5cd29786672dad1
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In Nuclear and High Energy Physics
Citations in the corpus
- Ultra high energy cosmic rays: implications of Auger data for source spectra and chemical composition (2013, methodology): “J C A P 1 0 ( 2 0 1 4 ) 0 2 0 The propagation of UHE nucleons1 is affected only by the interaction with the CMB radiation field [9, 10] and leads to the appearance of two spectral features: the pair-production dip [11, 12], which is a rather faint feature caused by the pair production process (p+γCM”
- Depth of Ultra High Energy Cosmic Ray Induced Air Shower Maxima Measured by the Telescope Array Black Rock and Long Ridge FADC Fluorescence Detectors and Surface Array in Hybrid Mode (2018, background): “See, for example, Aloisio et al. (2007) for further discussion of the dip model and the transition from galactic to extragalactic cosmic rays.”
- Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition (2011, methodology): “As discussed in [42], the dip model provides a suitable explanation of the observations provided that no more than ∼ 15%”