Impact of the magnetic horizon on the interpretation of the Pierre Auger Observatory spectrum and composition data

The Pierre Auger Collaboration

doi:10.1088/1475-7516/2024/07/094

Impact of the magnetic horizon on the interpretation of the Pierre Auger Observatory spectrum and composition data

The Pierre Auger Collaboration

Research output: Contribution to journal › Article › peer-review

1 Citation (Scopus)

Abstract

The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood in which the closest sources lie of order B_rms ≃ (50–100) nG (20 Mpc/d_s)(100 kpc/L_coh)¹/², with d_s the typical intersource separation and L_coh the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., ∝ E⁻². An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6 EeV.

Original language	English
Article number	094
Number of pages	31
Journal	Journal of Cosmology and Astroparticle Physics
Volume	2024
Issue number	7
DOIs	https://doi.org/10.1088/1475-7516/2024/07/094
Publication status	Published - 1 Jul 2024

Bibliographical note

Funding Information:
The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and administrative staff in Malarg\u00FCe. We are very grateful to the following agencies and organizations for financial support: Argentina \u2014 Comisi\u00F3n Nacional de Energ\u00EDa At\u00F3mica; Agencia Nacional de Promoci\u00F3n Cient\u00EDfica y Tecnol\u00F3gica (ANPCyT); Consejo Nacional de Investigaciones Cient\u00EDficas y T\u00E9cnicas (CONICET); Gobierno de la Provincia de Mendoza; Municipalidad de Malarg\u00FCe; NDM Holdings and Valle Las Le\u00F1as; in gratitude for their continuing cooperation over land access; Australia \u2014 the Australian Research Council; Belgium \u2014 Fonds de la Recherche Scientifique (FNRS); Research Foundation Flanders (FWO), Marie Curie Action of the European Union Grant No. 101107047; Brazil \u2014 Conselho Nacional de Desenvolvimento Cient\u00EDfico e Tecnol\u00F3gico (CNPq); Financiadora de Estudos e Projetos (FINEP); Funda\u00E7\u00E3o de Amparo \u00E0 Pesquisa do Estado de Rio de Janeiro (FAPERJ); S\u00E3o Paulo Research Foundation (FAPESP) Grants No. 2019/10151-2, No. 2010/07359-6 and No. 1999/05404-3; Minist\u00E9rio da Ci\u00EAncia, Tecnologia, Inova\u00E7\u00F5es e Comunica\u00E7\u00F5es (MCTIC); Czech Republic \u2014 GACR 24-13049S, CAS LQ100102401, MEYS LM2023032, CZ.02.1.01/0.0/0.0/16_013/0001402, CZ.02.1.01/0.0/0.0/18_046/0016010 and CZ.02.1.01/0.0/0.0/17_049/0008422 and CZ.02.01.01/00/22_008/0004632; France \u2014 Centre de Calcul IN2P3/CNRS; Centre National de la Recherche Scientifique (CNRS); Conseil R\u00E9gional Ile-de-France; D\u00E9partement Physique Nucl\u00E9aire et Corpusculaire (PNCIN2P3/CNRS); D\u00E9partement Sciences de l\u2019Univers (SDU-INSU/CNRS); Institut Lagrange de Paris (ILP) Grant No. LABEX ANR-10-LABX-63 within the Investissements d\u2019Avenir Programme Grant No. ANR-11-IDEX-0004-02; Germany \u2014 Bundesministerium f\u00FCr Bildung und Forschung (BMBF); Deutsche Forschungsgemeinschaft (DFG); Finanzministerium Baden-W\u00FCrttemberg; Helmholtz Alliance for Astroparticle Physics (HAP); Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF); Ministerium f\u00FCr Kultur und Wissenschaft des Landes Nordrhein-Westfalen; Ministerium f\u00FCr Wissenschaft, Forschung und Kunst des Landes Baden-W\u00FCrttemberg; Italy \u2014 Istituto Nazionale di Fisica Nucleare (INFN); Istituto Nazionale di Astrofisica (INAF); Ministero dell\u2019Universit\u00E0 e della Ricerca (MUR); CETEMPS Center of Excellence; Ministero degli Affari Esteri (MAE), ICSC Centro Nazionale di Ricerca in High Performance Computing, Big Data and Quantum Computing, funded by European Union NextGenerationEU, reference code CN_00000013; M\u00E9xico \u2014 Consejo Nacional de Ciencia y Tecnolog\u00EDa (CONACYT) No. 167733; Universidad Nacional Aut\u00F3noma de M\u00E9xico (UNAM); PAPIIT DGAPA-UNAM; The Netherlands \u2014 Ministry of Education, Culture and Science; Netherlands Organisation for Scientific Research (NWO); Dutch national e-infrastructure with the support of SURF Cooperative; Poland \u2014 Ministry of Education and Science, grants No. DIR/WK/2018/11 and 2022/WK/12; National Science Centre, grants No. 2016/22/M/ST9/00198, 2016/23/B/ST9/01635, 2020/39/B/ST9/01398, and 2022/45/B/ST9/02163; Portugal \u2014 Portuguese national funds and FEDER funds within Programa Operacional Factores de Competitividade through Funda\u00E7\u00E3o para a Ci\u00EAncia e a Tecnologia (COMPETE); Romania \u2014 Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, contract no. 30N/2023 under Romanian National Core Program LAPLAS VII, grant no. PN 23 21 01 02 and project number PN-III-P1-1.1-TE-2021-0924/TE57/2022, within PNCDI III; Slovenia \u2014 Slovenian Research Agency, grants P1-0031, P1-0385, I0-0033, N1-0111; Spain \u2014 Ministerio de Ciencia e Innovaci\u00F3n/Agencia Estatal de Investigaci\u00F3n (PID2019-105544GB-I00, PID2022-140510NB-I00 and RYC2019-027017-I), Xunta de Galicia (CIGUS Network of Research Centers, Consolidaci\u00F3n 2021 GRC GI-2033, ED431C-2021/22 and ED431F-2022/15), Junta de Andaluc\u00EDa (SOMM17/6104/UGR and P18-FR-4314), and the European Union (Marie Sklodowska-Curie 101065027 and ERDF); U.S.A. \u2014 Department of Energy, Contracts No. DE-AC02-07CH11359, No. DE-FR02-04ER41300, No. DE-FG02-99ER41107 and No. DE-SC0011689; National Science Foundation, Grant No. 0450696; The Grainger Foundation; Marie Curie-IRSES/EPLANET; European Particle Physics Latin American Network; and UNESCO.

Publisher Copyright:
© 2024 The Author(s).

Keywords

cosmic ray experiments
cosmic ray theory
ultra high energy cosmic rays

Access to Document

10.1088/1475-7516/2024/07/094

Cite this

@article{7279ae88f1ef4edca3a1f1a76893532a,

title = "Impact of the magnetic horizon on the interpretation of the Pierre Auger Observatory spectrum and composition data",

abstract = "The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood in which the closest sources lie of order Brms ≃ (50–100) nG (20 Mpc/ds)(100 kpc/Lcoh)1/2, with ds the typical intersource separation and Lcoh the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., ∝ E−2. An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6 EeV.",

keywords = "cosmic ray experiments, cosmic ray theory, ultra high energy cosmic rays",

author = "{The Pierre Auger Collaboration} and {Abdul Halim}, A. and P. Abreu and M. Aglietta and I. Allekotte and Cheminant, {K. Almeida} and A. Almela and R. Aloisio and J. Alvarez-Mu{\~n}iz and {Ammerman Yebra}, J. and Anastasi, {G. A.} and L. Anchordoqui and B. Andrada and S. Andringa and L. Apollonio and C. Aramo and {Ara{\'u}jo Ferreira}, {P. R.} and E. Arnone and {Arteaga Vel{\'a}zquez}, {J. C.} and P. Assis and G. Avila and E. Avocone and A. Bakalova and F. Barbato and {Bartz Mocellin}, A. and Bellido, {J. A.} and C. Berat and Bertaina, {M. E.} and G. Bhatta and M. Bianciotto and Biermann, {P. L.} and V. Binet and K. Bismark and T. Bister and J. Biteau and J. Blazek and C. Bleve and J. Bl{\"u}mer and M. Boh{\'a}{\v c}ov{\'a} and D. Boncioli and C. Bonifazi and S. Buitink and {de Jong}, {S. J.} and G. Golup and H{\"o}randel, {J. R.} and T. Huege and K. Mulrey and K. Nguyen and O. Scholten and K. Simkova and F. Simon",

note = "Funding Information: The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and administrative staff in Malarg\u00FCe. We are very grateful to the following agencies and organizations for financial support: Argentina \u2014 Comisi\u00F3n Nacional de Energ\u00EDa At\u00F3mica; Agencia Nacional de Promoci\u00F3n Cient\u00EDfica y Tecnol\u00F3gica (ANPCyT); Consejo Nacional de Investigaciones Cient\u00EDficas y T\u00E9cnicas (CONICET); Gobierno de la Provincia de Mendoza; Municipalidad de Malarg\u00FCe; NDM Holdings and Valle Las Le\u00F1as; in gratitude for their continuing cooperation over land access; Australia \u2014 the Australian Research Council; Belgium \u2014 Fonds de la Recherche Scientifique (FNRS); Research Foundation Flanders (FWO), Marie Curie Action of the European Union Grant No. 101107047; Brazil \u2014 Conselho Nacional de Desenvolvimento Cient\u00EDfico e Tecnol\u00F3gico (CNPq); Financiadora de Estudos e Projetos (FINEP); Funda\u00E7\u00E3o de Amparo \u00E0 Pesquisa do Estado de Rio de Janeiro (FAPERJ); S\u00E3o Paulo Research Foundation (FAPESP) Grants No. 2019/10151-2, No. 2010/07359-6 and No. 1999/05404-3; Minist\u00E9rio da Ci\u00EAncia, Tecnologia, Inova\u00E7\u00F5es e Comunica\u00E7\u00F5es (MCTIC); Czech Republic \u2014 GACR 24-13049S, CAS LQ100102401, MEYS LM2023032, CZ.02.1.01/0.0/0.0/16_013/0001402, CZ.02.1.01/0.0/0.0/18_046/0016010 and CZ.02.1.01/0.0/0.0/17_049/0008422 and CZ.02.01.01/00/22_008/0004632; France \u2014 Centre de Calcul IN2P3/CNRS; Centre National de la Recherche Scientifique (CNRS); Conseil R\u00E9gional Ile-de-France; D\u00E9partement Physique Nucl\u00E9aire et Corpusculaire (PNCIN2P3/CNRS); D\u00E9partement Sciences de l\u2019Univers (SDU-INSU/CNRS); Institut Lagrange de Paris (ILP) Grant No. LABEX ANR-10-LABX-63 within the Investissements d\u2019Avenir Programme Grant No. ANR-11-IDEX-0004-02; Germany \u2014 Bundesministerium f\u00FCr Bildung und Forschung (BMBF); Deutsche Forschungsgemeinschaft (DFG); Finanzministerium Baden-W\u00FCrttemberg; Helmholtz Alliance for Astroparticle Physics (HAP); Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF); Ministerium f\u00FCr Kultur und Wissenschaft des Landes Nordrhein-Westfalen; Ministerium f\u00FCr Wissenschaft, Forschung und Kunst des Landes Baden-W\u00FCrttemberg; Italy \u2014 Istituto Nazionale di Fisica Nucleare (INFN); Istituto Nazionale di Astrofisica (INAF); Ministero dell\u2019Universit\u00E0 e della Ricerca (MUR); CETEMPS Center of Excellence; Ministero degli Affari Esteri (MAE), ICSC Centro Nazionale di Ricerca in High Performance Computing, Big Data and Quantum Computing, funded by European Union NextGenerationEU, reference code CN_00000013; M\u00E9xico \u2014 Consejo Nacional de Ciencia y Tecnolog\u00EDa (CONACYT) No. 167733; Universidad Nacional Aut\u00F3noma de M\u00E9xico (UNAM); PAPIIT DGAPA-UNAM; The Netherlands \u2014 Ministry of Education, Culture and Science; Netherlands Organisation for Scientific Research (NWO); Dutch national e-infrastructure with the support of SURF Cooperative; Poland \u2014 Ministry of Education and Science, grants No. DIR/WK/2018/11 and 2022/WK/12; National Science Centre, grants No. 2016/22/M/ST9/00198, 2016/23/B/ST9/01635, 2020/39/B/ST9/01398, and 2022/45/B/ST9/02163; Portugal \u2014 Portuguese national funds and FEDER funds within Programa Operacional Factores de Competitividade through Funda\u00E7\u00E3o para a Ci\u00EAncia e a Tecnologia (COMPETE); Romania \u2014 Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, contract no. 30N/2023 under Romanian National Core Program LAPLAS VII, grant no. PN 23 21 01 02 and project number PN-III-P1-1.1-TE-2021-0924/TE57/2022, within PNCDI III; Slovenia \u2014 Slovenian Research Agency, grants P1-0031, P1-0385, I0-0033, N1-0111; Spain \u2014 Ministerio de Ciencia e Innovaci\u00F3n/Agencia Estatal de Investigaci\u00F3n (PID2019-105544GB-I00, PID2022-140510NB-I00 and RYC2019-027017-I), Xunta de Galicia (CIGUS Network of Research Centers, Consolidaci\u00F3n 2021 GRC GI-2033, ED431C-2021/22 and ED431F-2022/15), Junta de Andaluc\u00EDa (SOMM17/6104/UGR and P18-FR-4314), and the European Union (Marie Sklodowska-Curie 101065027 and ERDF); U.S.A. \u2014 Department of Energy, Contracts No. DE-AC02-07CH11359, No. DE-FR02-04ER41300, No. DE-FG02-99ER41107 and No. DE-SC0011689; National Science Foundation, Grant No. 0450696; The Grainger Foundation; Marie Curie-IRSES/EPLANET; European Particle Physics Latin American Network; and UNESCO. Publisher Copyright: {\textcopyright} 2024 The Author(s).",

year = "2024",

month = jul,

day = "1",

doi = "10.1088/1475-7516/2024/07/094",

language = "English",

volume = "2024",

journal = "Journal of Cosmology and Astroparticle Physics",

issn = "1475-7516",

publisher = "IOP Publishing Ltd.",

number = "7",

}

TY - JOUR

T1 - Impact of the magnetic horizon on the interpretation of the Pierre Auger Observatory spectrum and composition data

AU - The Pierre Auger Collaboration

AU - Abdul Halim, A.

AU - Abreu, P.

AU - Aglietta, M.

AU - Allekotte, I.

AU - Cheminant, K. Almeida

AU - Almela, A.

AU - Aloisio, R.

AU - Alvarez-Muñiz, J.

AU - Ammerman Yebra, J.

AU - Anastasi, G. A.

AU - Anchordoqui, L.

AU - Andrada, B.

AU - Andringa, S.

AU - Apollonio, L.

AU - Aramo, C.

AU - Araújo Ferreira, P. R.

AU - Arnone, E.

AU - Arteaga Velázquez, J. C.

AU - Assis, P.

AU - Avila, G.

AU - Avocone, E.

AU - Bakalova, A.

AU - Barbato, F.

AU - Bartz Mocellin, A.

AU - Bellido, J. A.

AU - Berat, C.

AU - Bertaina, M. E.

AU - Bhatta, G.

AU - Bianciotto, M.

AU - Biermann, P. L.

AU - Binet, V.

AU - Bismark, K.

AU - Bister, T.

AU - Biteau, J.

AU - Blazek, J.

AU - Bleve, C.

AU - Blümer, J.

AU - Boháčová, M.

AU - Boncioli, D.

AU - Bonifazi, C.

AU - Buitink, S.

AU - de Jong, S. J.

AU - Golup, G.

AU - Hörandel, J. R.

AU - Huege, T.

AU - Mulrey, K.

AU - Nguyen, K.

AU - Scholten, O.

AU - Simkova, K.

AU - Simon, F.

N1 - Funding Information: The successful installation, commissioning, and operation of the Pierre Auger Observatory would not have been possible without the strong commitment and effort from the technical and administrative staff in Malarg\u00FCe. We are very grateful to the following agencies and organizations for financial support: Argentina \u2014 Comisi\u00F3n Nacional de Energ\u00EDa At\u00F3mica; Agencia Nacional de Promoci\u00F3n Cient\u00EDfica y Tecnol\u00F3gica (ANPCyT); Consejo Nacional de Investigaciones Cient\u00EDficas y T\u00E9cnicas (CONICET); Gobierno de la Provincia de Mendoza; Municipalidad de Malarg\u00FCe; NDM Holdings and Valle Las Le\u00F1as; in gratitude for their continuing cooperation over land access; Australia \u2014 the Australian Research Council; Belgium \u2014 Fonds de la Recherche Scientifique (FNRS); Research Foundation Flanders (FWO), Marie Curie Action of the European Union Grant No. 101107047; Brazil \u2014 Conselho Nacional de Desenvolvimento Cient\u00EDfico e Tecnol\u00F3gico (CNPq); Financiadora de Estudos e Projetos (FINEP); Funda\u00E7\u00E3o de Amparo \u00E0 Pesquisa do Estado de Rio de Janeiro (FAPERJ); S\u00E3o Paulo Research Foundation (FAPESP) Grants No. 2019/10151-2, No. 2010/07359-6 and No. 1999/05404-3; Minist\u00E9rio da Ci\u00EAncia, Tecnologia, Inova\u00E7\u00F5es e Comunica\u00E7\u00F5es (MCTIC); Czech Republic \u2014 GACR 24-13049S, CAS LQ100102401, MEYS LM2023032, CZ.02.1.01/0.0/0.0/16_013/0001402, CZ.02.1.01/0.0/0.0/18_046/0016010 and CZ.02.1.01/0.0/0.0/17_049/0008422 and CZ.02.01.01/00/22_008/0004632; France \u2014 Centre de Calcul IN2P3/CNRS; Centre National de la Recherche Scientifique (CNRS); Conseil R\u00E9gional Ile-de-France; D\u00E9partement Physique Nucl\u00E9aire et Corpusculaire (PNCIN2P3/CNRS); D\u00E9partement Sciences de l\u2019Univers (SDU-INSU/CNRS); Institut Lagrange de Paris (ILP) Grant No. LABEX ANR-10-LABX-63 within the Investissements d\u2019Avenir Programme Grant No. ANR-11-IDEX-0004-02; Germany \u2014 Bundesministerium f\u00FCr Bildung und Forschung (BMBF); Deutsche Forschungsgemeinschaft (DFG); Finanzministerium Baden-W\u00FCrttemberg; Helmholtz Alliance for Astroparticle Physics (HAP); Helmholtz-Gemeinschaft Deutscher Forschungszentren (HGF); Ministerium f\u00FCr Kultur und Wissenschaft des Landes Nordrhein-Westfalen; Ministerium f\u00FCr Wissenschaft, Forschung und Kunst des Landes Baden-W\u00FCrttemberg; Italy \u2014 Istituto Nazionale di Fisica Nucleare (INFN); Istituto Nazionale di Astrofisica (INAF); Ministero dell\u2019Universit\u00E0 e della Ricerca (MUR); CETEMPS Center of Excellence; Ministero degli Affari Esteri (MAE), ICSC Centro Nazionale di Ricerca in High Performance Computing, Big Data and Quantum Computing, funded by European Union NextGenerationEU, reference code CN_00000013; M\u00E9xico \u2014 Consejo Nacional de Ciencia y Tecnolog\u00EDa (CONACYT) No. 167733; Universidad Nacional Aut\u00F3noma de M\u00E9xico (UNAM); PAPIIT DGAPA-UNAM; The Netherlands \u2014 Ministry of Education, Culture and Science; Netherlands Organisation for Scientific Research (NWO); Dutch national e-infrastructure with the support of SURF Cooperative; Poland \u2014 Ministry of Education and Science, grants No. DIR/WK/2018/11 and 2022/WK/12; National Science Centre, grants No. 2016/22/M/ST9/00198, 2016/23/B/ST9/01635, 2020/39/B/ST9/01398, and 2022/45/B/ST9/02163; Portugal \u2014 Portuguese national funds and FEDER funds within Programa Operacional Factores de Competitividade through Funda\u00E7\u00E3o para a Ci\u00EAncia e a Tecnologia (COMPETE); Romania \u2014 Ministry of Research, Innovation and Digitization, CNCS-UEFISCDI, contract no. 30N/2023 under Romanian National Core Program LAPLAS VII, grant no. PN 23 21 01 02 and project number PN-III-P1-1.1-TE-2021-0924/TE57/2022, within PNCDI III; Slovenia \u2014 Slovenian Research Agency, grants P1-0031, P1-0385, I0-0033, N1-0111; Spain \u2014 Ministerio de Ciencia e Innovaci\u00F3n/Agencia Estatal de Investigaci\u00F3n (PID2019-105544GB-I00, PID2022-140510NB-I00 and RYC2019-027017-I), Xunta de Galicia (CIGUS Network of Research Centers, Consolidaci\u00F3n 2021 GRC GI-2033, ED431C-2021/22 and ED431F-2022/15), Junta de Andaluc\u00EDa (SOMM17/6104/UGR and P18-FR-4314), and the European Union (Marie Sklodowska-Curie 101065027 and ERDF); U.S.A. \u2014 Department of Energy, Contracts No. DE-AC02-07CH11359, No. DE-FR02-04ER41300, No. DE-FG02-99ER41107 and No. DE-SC0011689; National Science Foundation, Grant No. 0450696; The Grainger Foundation; Marie Curie-IRSES/EPLANET; European Particle Physics Latin American Network; and UNESCO. Publisher Copyright: © 2024 The Author(s).

PY - 2024/7/1

Y1 - 2024/7/1

N2 - The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood in which the closest sources lie of order Brms ≃ (50–100) nG (20 Mpc/ds)(100 kpc/Lcoh)1/2, with ds the typical intersource separation and Lcoh the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., ∝ E−2. An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6 EeV.

AB - The flux of ultra-high energy cosmic rays reaching Earth above the ankle energy (5 EeV) can be described as a mixture of nuclei injected by extragalactic sources with very hard spectra and a low rigidity cutoff. Extragalactic magnetic fields existing between the Earth and the closest sources can affect the observed CR spectrum by reducing the flux of low-rigidity particles reaching Earth. We perform a combined fit of the spectrum and distributions of depth of shower maximum measured with the Pierre Auger Observatory including the effect of this magnetic horizon in the propagation of UHECRs in the intergalactic space. We find that, within a specific range of the various experimental and phenomenological systematics, the magnetic horizon effect can be relevant for turbulent magnetic field strengths in the local neighbourhood in which the closest sources lie of order Brms ≃ (50–100) nG (20 Mpc/ds)(100 kpc/Lcoh)1/2, with ds the typical intersource separation and Lcoh the magnetic field coherence length. When this is the case, the inferred slope of the source spectrum becomes softer and can be closer to the expectations of diffusive shock acceleration, i.e., ∝ E−2. An additional cosmic-ray population with higher source density and softer spectra, presumably also extragalactic and dominating the cosmic-ray flux at EeV energies, is also required to reproduce the overall spectrum and composition results for all energies down to 0.6 EeV.

KW - cosmic ray experiments

KW - cosmic ray theory

KW - ultra high energy cosmic rays

UR - http://www.scopus.com/inward/record.url?scp=85200904195&partnerID=8YFLogxK

U2 - 10.1088/1475-7516/2024/07/094

DO - 10.1088/1475-7516/2024/07/094

M3 - Article

AN - SCOPUS:85200904195

VL - 2024

JO - Journal of Cosmology and Astroparticle Physics

JF - Journal of Cosmology and Astroparticle Physics

SN - 1475-7516

IS - 7

M1 - 094

ER -

Impact of the magnetic horizon on the interpretation of the Pierre Auger Observatory spectrum and composition data

Abstract

Bibliographical note

Keywords

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