Impact of the Magnetic Horizon on the Interpretation of the Pierre Auger Observatory Spectrum and Composition Data

• Published in: arXiv.org
• Main Authors: Abreu, P, K Almeida Cheminant, Almela, A, Alvarez-Muñiz, J, J Ammerman Yebra, Aramo, C, Arteaga Velázquez, J C, Bhatta, G, Blazek, J, Boháčová, M, P G Brichetto Orchera, Buscemi, M, Büsken, M, Bwembya, A, Caballero-Mora, K S, Cabana-Freire, S, Caruso, R, Cermenati, A, Clay, R W, Cobos Cerutti, A C, Coluccia, M R, Condorelli, A, Covault, C E, Cruz Sanchez, C S, Dawson, B R, de Jesús, J, J R T de Mello Neto, de Oliveira Franco, D, Deligny, O, Dobre, M, dos Anjos, R C, Ellwanger, F, Farrar, G, Fauth, A C, Fernandes, A, Fitoussi, T, García, B, Gollan, F, González, N, Gottowik, M, Guido, E, Hamal, P, Harvey, V M, Horvath, P, Hrabovský, M, Jilek, V, V V Kizakke Covilakam, Letessier-Selvon, A, Luce, Q, Lundquist, J P, A Machado Payeras, Mantsch, P, Martello, D, Martins, M A, Matthews, J, Mayotte, E, Mayotte, S, Mazur, P O, Menshikov, A, Micheletti, M I, Miramonti, L, Mussa, R, Nitz, D, Nucita, A, Panja, S, Parente, G, Pech, M, Pękala, J, Pelayo, R, Pereira Martins, E E, C Pérez Bertolli, Petrera, S, Reininghaus, M, Ridky, J, Saftoiu, A, Saharan, M, Salamida, F, Sato, R, Scherini, V, Schimassek, M, Schovánek, P, Schulte, J, Simkova, K, Smau, R, Sommers, P, Stassi, P, Svozilikova, Z, Szadkowski, Z, Tairli, F, Tobiska, P, Tomé, B, Travaini, A, Unger, M, Valdés Galicia, J F, Valore, L, Varela, E, Vergara Quispe, I D, Vicha, J, Vorobiov, S, Zavrtanik, D
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 01.08.2024
• Subjects: Augers; Coherence length; Composition; Cosmic rays; Earth; Horizon; Magnetic fields; Observatories; Physics - High Energy Astrophysical Phenomena; Rigidity; Spectra
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.2404.03533

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 of order \(B_{\rm rms}\simeq (50-100)\,{\rm nG}\,(20\rm{Mpc}/{d_{\rm s})( 100\,\rm{kpc}/L_{\rm coh}})^{1/2}\), with \(d_{\rm s}\) the typical intersource separation and \(L_{\rm coh}\) 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., \(\propto E^{-2}\). 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.