Search for Ultra-high-energy Neutrons from Galactic Sources with the Pierre Auger Observatory

Authors

• A. Abdul Halim, University of Adelaide
• P. Abreu, Universidade de Lisboa
• M. Aglietta, Osservatorio Astrofisico di Torino (INAF)
• I. Allekotte, Centro Atómico Bariloche and Instituto Balseiro (CNEA-UNCuyo-CONICET)
• K. Almeida Cheminant, Nationaal Instituut voor Kernfysica en Hoge Energie Fysica (NIKHEF)
• A. Almela, Instituto de Tecnologías en Detección y Astropartículas (CNEA, CONICET, UNSAM)
• B. Fick, Michigan Technological UniversityFollow
• K. Nguyen, Michigan Technological UniversityFollow
• D. Nitz, Michigan Technological UniversityFollow

Document Type

Article

Publication Date

3-2-2026

Department

Department of Physics

Abstract

Deflections in the propagation of charged ultra-high-energy cosmic rays (UHECRs) caused by magnetic fields make the identification of their sources challenging. On the other hand, the arrival directions at Earth of neutrons point directly to their origin. The emission of UHECRs from a source is expected to be accompanied by the production of neutrons in its vicinity through interactions with ambient matter and radiation. Since free neutrons travel a mean distance d kpc−1 = 9.2 (E EeV−1) before decaying, a neutron flux in the EeV range could be detected on Earth from sources of UHECRs in our Galaxy. Using cosmic-ray data from Phase I of the Surface Detector of the Pierre Auger Observatory, we search for neutron fluxes from Galactic candidate sources. We select more than 1000 objects of astrophysical interest, stacking them into target sets. The targets all have decl. within the exposure of the Observatory, ranging from −90° up to +45° for energies above 1 EeV (and up to +20° for energies down to 0.1 EeV). Given that a neutron air shower is indistinguishable from a proton one, there is a significant background due to cosmic rays. A neutron flux from the direction of a candidate source would be identified by a celestial density of events that significantly exceeds the expected density of cosmic rays for that direction. No significant excess is found at any tested target direction, and an upper limit on the neutron flux is calculated for each candidate source.

Publisher's Statement

© 2026. The Author(s). Published by the American Astronomical Society. Publisher’s version of record: https://doi.org/10.3847/1538-4357/ae3f05

Publication Title

The Astrophysical Journal

Recommended Citation

Halim, A. A., Abreu, P., Aglietta, M., Allekotte, I., Cheminant, K. A., Almela, A., Fick, B., Nguyen, K., & Nitz, D. (2026). Search for Ultra-high-energy Neutrons from Galactic Sources with the Pierre Auger Observatory. The Astrophysical Journal. http://doi.org/https://doi.org/10.3847/1538-4357/ae3f05
Retrieved from: https://digitalcommons.mtu.edu/michigantech-p2/2796

Version

Publisher's PDF