On astrophysical solution to ultrahigh energy cosmic rays

By V. Berezinsky, A. Gazizov, S. Grigorieva. 2002

396 citations recorded by the source corpus.

We argue that an astrophysical solution to the ultrahigh energy cosmic ray (UHECR) problem is viable. The detailed study of UHECR energy spectra is performed. The spectral features of extragalactic protons interacting with the cosmic microwave background (CMB) are calculated in a model-independent way. Using the power-law generation spectrum $\ensuremath{\propto}{E}^{\ensuremath{-}{\ensuremath{\gamma}}_{g}}$ as the only assumption, we analyze four features of the proton spectrum: the GZK cutoff, dip, bump, and the second dip. We found the dip, induced by electron-positron production on the CMB, to be the most robust feature, existing in energy range $1\ifmmode\times\else\texttimes\fi{}{10}^{18}\char21{}4\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{eV}$. Its shape is stable relative to various phenomena included in calculations: discreteness of the source distribution, different modes of UHE proton propagation (from rectilinear to diffusive), local overdensity or deficit of the sources, large-scale inhomogeneities in the universe, and interaction fluctuations. The dip is well confirmed by observations of the AGASA, HiRes, Fly's Eye, and Yakutsk detectors. With two free parameters (${\ensuremath{\gamma}}_{g}$ and flux normalization constant) the dip describes about 20 energy bins with ${\ensuremath{\chi}}^{2}/\mathrm{d}.\mathrm{o}.\mathrm{f}.\ensuremath{\approx}1$ for each experiment. The best fit is reached at ${\ensuremath{\gamma}}_{g}=2.7$, with the allowed range 2.55\char21{}2.75. The dip is used for energy calibration of the detectors. For each detector independently, the energy is shifted by factor $\ensuremath{\lambda}$ to reach the minimum ${\ensuremath{\chi}}^{2}$. We found ${\ensuremath{\lambda}}_{\mathrm{Ag}}=0.9$, ${\ensuremath{\lambda}}_{\mathrm{Hi}}=1.2$, and ${\ensuremath{\lambda}}_{\mathrm{Ya}}=0.75$ for the AGASA, HiRes, and Yakutsk detectors, respectively. Remarkably, after this energy shift the fluxes and spectra of all three detectors agree perfectly, with discrepancy between AGASA and HiRes at $Eg1\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{eV}$ being not statistically significant. The excellent agreement of the dip with observations should be considered as confirmation of UHE proton interaction with the CMB. The dip has two flattenings. The high energy flattening at $E\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{19}\text{ }\text{ }\mathrm{eV}$ automatically explains ankle, the feature observed in all experiments starting from the 1980s. The low-energy flattening at $E\ensuremath{\approx}1\ifmmode\times\else\texttimes\fi{}{10}^{18}\text{ }\text{ }\mathrm{eV}$ reproduces the transition to galactic cosmic rays. This transition is studied quantitatively in this work. Inclusion of primary nuclei with a fraction of more than 20% upsets the agreement of the dip with observations, which we interpret as an indication of the acceleration mechanism. We study in detail the formal problems of spectra calculations: energy losses (the new detailed calculations are presented), the analytic method of spectrum calculations, and the study of fluctuations with the help of a kinetic equation. The UHECR sources, AGN and GRBs, are studied in a model-dependent way, and acceleration is discussed. Based on the agreement of the dip with existing data, we make the robust prediction for the spectrum at $1\ifmmode\times\else\texttimes\fi{}{10}^{18}\char21{}1\ifmmode\times\else\texttimes\fi{}{10}^{20}\text{ }\text{ }\mathrm{eV}$ to be measured in the nearest future by the Auger detector. We also predict the spectral signature of nearby sources, if they are observed by Auger. This paper is long and contains many technical details. For those who are interested only in physical content we recommend the Introduction and Conclusions, which are written as autonomous parts of the paper.

Subfields: Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/53a853243ef097ddffb5b5a8f856200c597a008b

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Citations in the corpus

• Ultra high energy cosmic rays: implications of Auger data for source spectra and chemical composition (2013, background): “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”
• ROLE OF LINE-OF-SIGHT COSMIC-RAY INTERACTIONS IN FORMING THE SPECTRA OF DISTANT BLAZARS IN TeV GAMMA RAYS AND HIGH-ENERGY NEUTRINOS (2010, methodology): “We have obtained an excellent fit for each of the three blazars using some reasonable values of cosmic-ray power, consistent with theoretical models of cosmic rays (Berezinsky et al. 2006).”
• A new interpretation of the gamma-ray observations of distant active galactic nuclei (2009, methodology): “y pγ interactions at z = 0.28 (the spectrum with a lower mean energy) and z = 0.014 (the spectrum with a higher mean) by protons emitted from the source at z = 0.444 (e.g., 3C66A) with a E−2 spectrum [22]. The units are arbitrary, and the upper curve is scaled down by a factor 10. We have calculated”
• SPECTRUM OF GALACTIC COSMIC RAYS ACCELERATED IN SUPERNOVA REMNANTS (2010, background): “This is important in light of the discussion about transition from the Galactic to extragalactic component in the observed cosmic ray spectrum (Berezinsky et al. 2006; Hillas 2006).”
• The Astrophysics of Ultrahigh-Energy Cosmic Rays (2011, background): “The effect of photo-hadronic interactions on the cosmic ray spectrum can be calculated analytically for protons (Berezinsky & Grigorieva 1988; Berezinsky et al. 2006).”
• Cosmogenic neutrinos: parameter space and detectabilty from PeV to ZeV (2010, background): “Again in this scenario, heavy elements cannot exceed 10-15% of the total composition in order to fit the shape of the spectrum (Berezinsky et al., 2006; Allard et al., 2007).”
• Cosmic-ray energy spectrum and composition up to the ankle - the case for a second Galactic component (2016, methodology): “…the Pierre Auger Collaboration (Aab et al. 2014) has raised problems with this approach, as the model is compatible only with more than 80% protons (Berezinsky et al. 2006), a number of new models have been suggested, involving compact sources with significant photo-disintegration of nuclei…”
• Open Questions in Cosmic-Ray Research at Ultrahigh Energies (2019, neutral): “The energy production rate of UHECRs has been estimated in Waxman (1995b), Berezinsky et al. (2006), Katz et al. (2009), and Murase and Takami (2009) under the assumption that UHECRs are extragalactic protons.”
• BLAZARS AS ULTRA-HIGH-ENERGY COSMIC-RAY SOURCES: IMPLICATIONS FOR TeV GAMMA-RAY OBSERVATIONS (2011, background): “If comparable power goes into the acceleration of UHECRs, then BL Lac objects and FR-I radio galaxies have more than sufficient emissivity to power the& 10 EeV UHECRs, which require ∼ 1044 erg Mpc−3 yr−1 (Waxman & Bahcall 1999; Berezinsky et al. 2006; Murase & Takami 2009).”