722 research outputs found
Probing Lorentz symmetry with the Pierre Auger Observatory
No full textEffects of Lorentz invariance violation (LIV) can be present at energies much lower than the quantum gravity scale. Here the possible LIV effects in ultra-high energy cosmic rays (UHECRs) are investigated. To this aim, modifications of the propagation of UHECR protons and nuclei in the extragalactic space due to LIV effects are taken into account. For the first time a fit of both flux and composition of UHECRs as measured by the Pierre Auger Observatory is used in order to evaluate the constraining power of current data on LIV parameters
Interactions of Cosmic Rays around the Universe. Models for UHECR data interpretation
No full textUltra high energy cosmic rays (UHECRs) are expected to be accelerated inastrophysical sources and to travel through extragalactic space before hitting the Earth atmosphere.They interact both with the environment in the source and with the intergalacticphoton fields they encounter, causing different processes at various scales dependingon the photon energy in the nucleus rest frame. UHECR interactions are sensitive touncertainties in the extragalactic background spectrum and in the photo-disintegrationmodels
Cosmic ray composition studies with the Pierre Auger Observatory
No full textThe Pierre Auger Observatory in Argentina is the largest cosmic ray detector array ever built. Although the construction was completed in 2008, the Observatory has been taking data continuously since January 2004. Its main goal is to measure ultra high energy cosmic rays (UHECRs, energy above 10 18 eV) with unprecedented statistics and precision. Measurements of the energy spectrum, chemical composition (including neutrinos and photons) and arrival directions of UHECRs can provide hints for understanding their origin, propagation and interactions. The fluorescence detector of the Pierre Auger Observatory measures the atmospheric depth, Xmax, where the longitudinal profile of a high energy air shower reaches its maximum. This is sensitive to the nuclear mass composition of the cosmic ray and to the characteristics of the hadronic interactions at very high energy. Due to its hybrid design, the Pierre Auger Observatory also provides independent experimental observables obtained from the surface detector for the study of the shower development. A selection of the Pierre Auger Observatory results on the study of the UHECRs will be presented, focusing on composition results. In particular, the measurements and the different roles of the observables with respect to mass composition will be discussed. © 2013 Elsevier B.V
Measurement of the energy spectrum of cosmic rays using the Pierre Auger Observatory
No full textThe flux of cosmic rays above 1018 eV has been measured with unprecedented precision at the Pierre Auger Observatory. Two analysis techniques have been used to extend the spectrum downwards from 3 × 1018 eV, with the lower energies being explored using a unique technique that exploits the hybrid strengths of the instrument. The spectral features are also presented. © Società Italiana di Fisica
Ultra High Energy Cosmic Rays: Anisotropies and spectrum
No full textThe recent results of the Pierre Auger Observatory on the possible correlation of Ultra High Energy Cosmic Rays events and several nearby discrete sources could be the starting point of a new era with charged particles astronomy. In this paper we introduce a simple model to determine the effects of any local distribution of sources on the expected flux. We consider two populations of sources: faraway sources uniformly distributed and local point sources. We study the effects on the expected flux of the local distribution of sources, referring also to the set of astrophysical objects whose correlation with the Auger events is experimentally claimed. © 2011 Elsevier B.V. All rights reserved
On the common origin of cosmic rays across the ankle and diffuse neutrinos at the highest energies from low-luminosity Gamma-Ray Bursts
No full textWe demonstrate that the UHECRs produced in the nuclear cascade in the jet of Low-Luminosity Gamma-Ray Bursts (LL-GRBs) can describe the UHECR spectrum and composition and, at the same time, the diffuse neutrino flux at the highest energies. The radiation density in the source simultaneously controls the neutrino production and the development of the nuclear cascade, leading to a flux of nucleons and light nuclei describing even the cosmic-ray ankle at eV. The derived source parameters are consistent with population studies, indicating a baryonic loading factor of about ten. Our results motivate the continued experimental search of LL-GRBs as a unique GRB population
Surprises from extragalactic propagation of UHECRs
No full textUltra-high energy cosmic ray experimental data are now of very good statistical significance even in the region of the expected GZK feature. The identification of their sources requires sophisticate analysis of their propagation in the extragalactic space. When looking at the details of this propagation some unforeseen features emerge. We will discuss some of these “surprises”
Nuclear Physics Meets the Sources of the Ultra-High Energy Cosmic Rays
No full textThe determination of the injection composition of cosmic ray nuclei within astrophysical sources requires sufficiently accurate descriptions of the source physics and the propagation - apart from controlling astrophysical uncertainties. We therefore study the implications of nuclear data and models for cosmic ray astrophysics, which involves the photo-disintegration of nuclei up to iron in astrophysical environments. We demonstrate that the impact of nuclear model uncertainties is potentially larger in environments with non-thermal radiation fields than in the cosmic microwave background. We also study the impact of nuclear models on the nuclear cascade in a gamma-ray burst radiation field, simulated at a level of complexity comparable to the most precise cosmic ray propagation code. We conclude with an isotope chart describing which information is in principle necessary to describe nuclear interactions in cosmic ray sources and propagation
Nuclear physics aspects of relevance to the sources of UHECRs
No full textAlthough the accelerators of ultra-high energy cosmic rays (UHECR) are still not identified, we have new hope to constrain their properties using a multi-messenger approach. Every astrophysical environment, where UHECR nuclei are accelerated and interact with the dense photon fields, will also emit neutrinos. This depends on several modeling aspects of the related photo-nuclear physics in the energy range of the Giant Dipole Resonance and the Quasi Deuteron processes, and also in a regime where the production of pions occurs, which eventually will decay into neutrinos. We have studied in detail the properties of nuclear disintegration rates and chains inside candidate accelerators and during the extragalactic propagation of UHECR. We find that over-simplified models of nuclear interactions, which are often used in UHECR propagation codes and source models, have noticeable impact on the theoretical description of the source and they can introduce a systematic bias to analyses based on statistical arguments. These additional uncertainties can be potentially resolved with accelerator measurements
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