High Energy Cosmic Ray and Neutrino Astronomy

Abstract

Cosmic-rays with energies exceeding 10 19 eV are referred to as Ultra High Energy Cosmic Rays (UHECRs). The sources of these particles and their acceleration mechanism are unknown, and for many years have been the issue of much debate. The first part of this review describes the main constraints, that are implied by UHECR observations on the properties of candidate UHECR sources, the candidate sources, and the related main open questions. In order to address the challenges of identifying the UHECR sources and of probing the physical mechanisms driving them, a "multi-messenger" approach will most likely be required, combining electromagnetic, cosmic-ray and neutrino observations. The second part of the review is devoted to a discussion of high energy neutrino astronomy. It is shown that detectors, which are currently under construction, are expected to reach the effective mass required for the detection of high energy extra-Galactic neutrino sources, and may therefore play a key role in the near future in resolving the main open questions. The detection of high energy neutrinos from extra-Galactic sources will not only provide constraints on the identity and underlying physics of UHECR sources, but may furthermore provide information on fundamental neutrino properties.

The Latest IceCube Results and the Implications

“…The first evidence of the astrophysical neutrinos has been found. The best-fit differential spectral index for the observed astrophysical neutrinos is −2.2 ± 0.4, and the best-fit all-flavor flux is derived as E 2 ϕ(E) = (3.6 ± 1.2) × 10 −8 GeV cm −2 s −1 sr −1 which is very close to the level of WB bound flux [21,22]. The observation suggests that the energy spectrum should have a cutoff or a break at PeV energies since the best-fit flux would expect an additional 3-6 events in the 2-10 PeV energy range.…”

“…Therefore, this analysis is only sensitive to muon flavor neutrinos. The sensitivity of this search is below Waxman-Bahcall (WB) bound [21,22], the expected maximum neutrino flux from the current cosmic-ray flux observation. A small excess (1.8σ) from the background at high energy was observed.…”

Icecube Observatory: Neutrinos and the Origin of Cosmic Rays

“…From this point of view, the current developments toward a radio array in Antarctica, such as Askaryan Radio Array (ARA) [51] is a natural extension toward the highest energies. [39,40,41,18,16,42,43,44,45,46,47] [48,49,50]. The sensitivity curves are evaluated at each decade of energy.…”

Optimization of ARIANNA station configuration

“…The bulk of these neutrinos will be observed with E ~ 10 18 -10 19 eV. The target sensitivity of the first Generation ARIANNA is sufficient to observe a flux or rule out the hypothesis that all cosmic rays at extreme energies are protons and extragalactic, independent of many of the astrophysical details such as source evolution, cosmology, and injection spectra at the source [7]. A nearly equally important goal of ARIANNA will be to extend the energy spectrum of the isotropic diffuse flux IceCube events [8] to energies above 10 16 eV.…”