![]() These quantities seem to be compatible with the distance, direction, and power (observed at MeV gamma energies) of the Seyfert galaxy MCG 8-11-11. Here we consider the conversion efficiency, ramifications, and energetics of these chain reactions for the 1991 October CR event at 320 EeV observed by the Fly's Eye detector in Utah. UHE photons or protons, secondaries of ν-νr scattering, might be the final observed signatures of such high-energy chain reactions, and may be responsible for the highest energy extragalactic cosmic-ray (CR) events. However, these UHE ν's may interact with others (mainly the heaviest: νμr, ντr, and respective antineutrinos) that are clustered into hot dark matter (HDM) galactic halos. Finally, we show that the number of UHE-induced tau air-shower events is larger at energies lower than Enu~1020 or Enu~1019 eV therefore we suggest an extension of the EUSO sensitivity at the lowest possible energy.ĭiffuse relic neutrinos with light mass are transparent to ultra-high-energy (UHE) neutrinos at thousands of EeV, which are born through the photoproduction of pions by UHE protons on relic 2.73 K blackbody radiation (BBR), and originate in active galactic nuclei (AGNs) at cosmic distances. Such a high angular resolution is necessary to disentangle tau air showers from more abundant downward horizontal UHECRs. In this picture, the Auger experiment might reveal such an increase at Enu~=1018 eV (with 26 events in 3 yr) if the angular resolution (both in azimuth and zenith) reaches an accuracy of nearly 1° (or below) the angular accuracy depends on the the morphology of the Andes, the distance of each element of the array from the mountain range, and the local terrestrial magnetic fields. Therefore, we expect an enhancement of neutrino detection along continental shelves near the highest mountain ranges, because of the better geometrical acceptance of Earth-skimming neutrinos. We also find that the equivalent mass for an outer layer made of rock is larger than the water mass, contrary to simplified all-rock/all-water Earth models and previous studies. The detection of HORTAUs may test the ``guaranteed'' GZK neutrino flux (secondaries of photopion production due to ultra-high-energy cosmic-ray scattering onto 2.75 K cosmic background radiation). Adopting simple power-law neutrino fluxes, dNnu/dEnu~E-2 and E-1, calibrated to Greisen-Zapetin-Kuzmin (GZK) like and Z-burst-like models, we estimate that at E~=1019 eV, nearly half a dozen horizontal shower events should be detected by EUSO in 3 yr of data collection, considering the 10% duty cycle efficiency and a minimal tau neutrino energy fluence phinuEnu~=50 eV cm-2 s-1 sr-1. ![]() The resulting model-independent effective masses for EUSO may encompass-at Enutau~=1019 eV-a huge average volume (~=1020 km3) compared to current neutrino experiments. Using a compact analytical formula, we calculate the effective target volumes and masses for tau air showers emerging from the Earth. Our result applies to most neutrino telescope projects, especially to the Extreme Universe Space Observatory (EUSO). We estimate the rate of observable horizontal and upward tau air showers (HORTAUs and UPTAUs, respectively) considering both the Earth's opacity and the contribution of the terrestrial atmosphere. The origin of the indicated deviation from isotropy is examined and prospects for more sensitive future studies are discussed. The three alternative models are favored against isotropy with 2.7-3.2 sigma significance. It is found that the starburst model fits the data better than the hypothesis of isotropy with a statistical significance of 4.0 sigma, the highest value of the test statistic being for energies above 39 EeV. A maximum-likelihood ratio test is used to evaluate the best values of these parameters and to quantify the strength of each model by contrast with isotropy. The sky model of cosmic-ray density constructed using each catalog has two free parameters, the fraction of events correlating with astrophysical objects and an angular scale characterizing the clustering of cosmic rays around extragalactic sources. ![]() Flux-limited samples, which include all types of galaxies from the Swift-BAT and 2MASS surveys, have been investigated for comparison. Sky models have been created for two distinct populations of extragalactic gamma-ray emitters: active galactic nuclei from the second catalog of hard Fermi-LAT sources (2FHL) and starburst galaxies from a sample that was examined with Fermi-LAT. The data consist of 5514 events above 20 EeV with zenith angles up to 80 deg recorded before 2017 April 30. A new analysis of the dataset from the Pierre Auger Observatory provides evidence for anisotropy in the arrival directions of ultra-high-energy cosmic rays on an intermediate angular scale, which is indicative of excess arrivals from strong, nearby sources.
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