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Title: Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory

Abstract

We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 ⋅ 10{sup 18} eV, i.e. the region of the all-particle spectrum above the so-called 'ankle' feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show that uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results.

Authors:
 [1]; ;  [2];  [3];  [4];  [5];  [6]; ;  [7];  [8];  [9];  [10];  [11];
  1. Institute for Mathematics, Astrophysics and Particle Physics (IMAPP), Radboud Universiteit, Nijmegen (Netherlands)
  2. Laboratório de Instrumentação e Física Experimental de Partículas—LIP and Instituto Superior Técnico—IST, Universidade de Lisboa—UL (Portugal)
  3. Osservatorio Astrofisico di Torino (INAF), Torino (Italy)
  4. Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Universités Paris 6 et Paris 7, CNRS-IN2P3 (France)
  5. Universidade de São Paulo, Inst. de Física, São Paulo (Brazil)
  6. Centro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET) (Argentina)
  7. Instituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM), Centro Atómico Constituyentes, Comisión Nacional de Energía Atómica (Argentina)
  8. Universidad Nacional Autónoma de México, México (Mexico)
  9. Universidad de Santiago de Compostela (Spain)
  10. Gran Sasso Science Institute (INFN), L'Aquila (Italy)
  11. Department of Physics and Astronomy, Lehman College, City University of New York (United States)
Publication Date:
OSTI Identifier:
22679904
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 04; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ASTROPHYSICS; COSMIC RADIATION; COSMIC SHOWERS; COSMOLOGICAL MODELS; ENERGY SPECTRA; INJECTION; MASS; NUCLEI

Citation Formats

Aab, A., Abreu, P., Andringa, S., Aglietta, M., Samarai, I. Al, Albuquerque, I.F.M., Allekotte, I., Almela, A., Andrada, B., Castillo, J. Alvarez, Alvarez-Muñiz, J., Anastasi, G.A., Anchordoqui, L., E-mail: auger_spokespersons@fnal.gov, and and others. Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/04/038.
Aab, A., Abreu, P., Andringa, S., Aglietta, M., Samarai, I. Al, Albuquerque, I.F.M., Allekotte, I., Almela, A., Andrada, B., Castillo, J. Alvarez, Alvarez-Muñiz, J., Anastasi, G.A., Anchordoqui, L., E-mail: auger_spokespersons@fnal.gov, & and others. Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory. United States. doi:10.1088/1475-7516/2017/04/038.
Aab, A., Abreu, P., Andringa, S., Aglietta, M., Samarai, I. Al, Albuquerque, I.F.M., Allekotte, I., Almela, A., Andrada, B., Castillo, J. Alvarez, Alvarez-Muñiz, J., Anastasi, G.A., Anchordoqui, L., E-mail: auger_spokespersons@fnal.gov, and and others. Sat . "Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory". United States. doi:10.1088/1475-7516/2017/04/038.
@article{osti_22679904,
title = {Combined fit of spectrum and composition data as measured by the Pierre Auger Observatory},
author = {Aab, A. and Abreu, P. and Andringa, S. and Aglietta, M. and Samarai, I. Al and Albuquerque, I.F.M. and Allekotte, I. and Almela, A. and Andrada, B. and Castillo, J. Alvarez and Alvarez-Muñiz, J. and Anastasi, G.A. and Anchordoqui, L., E-mail: auger_spokespersons@fnal.gov and and others},
abstractNote = {We present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 ⋅ 10{sup 18} eV, i.e. the region of the all-particle spectrum above the so-called 'ankle' feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show that uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results.},
doi = {10.1088/1475-7516/2017/04/038},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 04,
volume = 2017,
place = {United States},
year = {Sat Apr 01 00:00:00 EDT 2017},
month = {Sat Apr 01 00:00:00 EDT 2017}
}
  • In this paper, we present a combined fit of a simple astrophysical model of UHECR sources to both the energy spectrum and mass composition data measured by the Pierre Auger Observatory. The fit has been performed for energies above 5 • 10 18 eV, i.e. the region of the all-particle spectrum above the so-called 'ankle' feature. The astrophysical model we adopted consists of identical sources uniformly distributed in a comoving volume, where nuclei are accelerated through a rigidity-dependent mechanism. The fit results suggest sources characterized by relatively low maximum injection energies, hard spectra and heavy chemical composition. We also show thatmore » uncertainties about physical quantities relevant to UHECR propagation and shower development have a non-negligible impact on the fit results.« less
  • The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies E > E{sub th} = 5.5 × 10{sup 19} eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at E > E{sub th} are heavy nuclei with charge Z, the proton component of the sources should lead to excesses in the same regions at energies E/Z. We here report the lack of anisotropies in these directions at energies abovemore » E{sub th}/Z (for illustrative values of Z = 6,13,26). If the anisotropies above E{sub th} are due to nuclei with charge Z, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies.« less
  • The Pierre Auger Collaboration has reported evidence for anisotropy in the distribution of arrival directions of the cosmic rays with energies E > E th = 5.5 x 10 19 eV. These show a correlation with the distribution of nearby extragalactic objects, including an apparent excess around the direction of Centaurus A. If the particles responsible for these excesses at E > E th are heavy nuclei with charge Z, the proton component of the sources should lead to excesses in the same regions at energies E/Z. We here report the lack of anisotropies in these directions at energies abovemore » E th/Z (for illustrative values of Z = 6,13,26). If the anisotropies above E th are due to nuclei with charge Z, and under reasonable assumptions about the acceleration process, these observations imply stringent constraints on the allowed proton fraction at the lower energies.« less
  • We present the results of an analysis of data recorded at the Pierre Auger Observatory in which we search for groups of directionally-aligned events (or ''multiplets'') which exhibit a correlation between arrival direction and the inverse of the energy. These signatures are expected from sets of events coming from the same source after having been deflected by intervening coherent magnetic fields. The observation of several events from the same source would open the possibility to accurately reconstruct the position of the source and also measure the integral of the component of the magnetic field orthogonal to the trajectory of themore » cosmic rays. We describe the largest multiplets found and compute the probability that they appeared by chance from an isotropic distribution. We find no statistically significant evidence for the presence of multiplets arising from magnetic deflections in the present data.« less
  • To interpret the mean depth of cosmic ray air shower maximum and its dispersion, we parametrize those two observables as functions of the first two moments of the ln A distribution. We examine the goodness of this simple method through simulations of test mass distributions. The application of the parameterization to Pierre Auger Observatory data allows one to study the energy dependence of the mean ln A and of its variance under the assumption of selected hadronic interaction models. We discuss possible implications of these dependences in term of interaction models and astrophysical cosmic ray sources.