Origin of ultra-high-energy galactic cosmic rays the isotropy problem
- We study the propagation of ultra-high-energy cosmic rays (UHECRs) in the Galaxy, concentrating on the energy range below the ankle in the spectrum at 4 EeV. A Monte Carlo method, based on analytical solutions to the time-dependent diffusion problem, is used to account for intermittency by placing sources at random locations. Assuming a source population that scales with baryon mass density or star formation (e.g., long GRB), we derive constraints arising from intermittency and the observational limits on the composition and anisotropy. It is shown that the composition and anisotropy at 10(18) eV are difficult to reproduce and require that either (1) the particle mean free path is much smaller than a gyroradius, implying the escape time is very long, (2) the composition is heavier than suggested by recent Auger data, (3) the ultra-high-energy sub-ankle component is mostly extragalactic, or (4) we are living in a rare lull in the UHECR production, and the current UHECR intensity is far below the Galactic time average. We thereforeWe study the propagation of ultra-high-energy cosmic rays (UHECRs) in the Galaxy, concentrating on the energy range below the ankle in the spectrum at 4 EeV. A Monte Carlo method, based on analytical solutions to the time-dependent diffusion problem, is used to account for intermittency by placing sources at random locations. Assuming a source population that scales with baryon mass density or star formation (e.g., long GRB), we derive constraints arising from intermittency and the observational limits on the composition and anisotropy. It is shown that the composition and anisotropy at 10(18) eV are difficult to reproduce and require that either (1) the particle mean free path is much smaller than a gyroradius, implying the escape time is very long, (2) the composition is heavier than suggested by recent Auger data, (3) the ultra-high-energy sub-ankle component is mostly extragalactic, or (4) we are living in a rare lull in the UHECR production, and the current UHECR intensity is far below the Galactic time average. We therefore recommend a strong observational focus on determining the UHECR composition around 10(18) eV.…
Verfasserangaben: | Martin PohlORCiDGND, David Eichler |
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DOI: | https://doi.org/10.1088/0004-637X/742/2/114 |
ISSN: | 0004-637X |
Titel des übergeordneten Werks (Englisch): | The astrophysical journal : an international review of spectroscopy and astronomical physics |
Verlag: | IOP Publ. Ltd. |
Verlagsort: | Bristol |
Publikationstyp: | Wissenschaftlicher Artikel |
Sprache: | Englisch |
Jahr der Erstveröffentlichung: | 2011 |
Erscheinungsjahr: | 2011 |
Datum der Freischaltung: | 26.03.2017 |
Freies Schlagwort / Tag: | cosmic rays; gamma-ray burst: general |
Band: | 742 |
Ausgabe: | 2 |
Seitenanzahl: | 11 |
Fördernde Institution: | Israel Science Foundation; Israel-U.S. Binational Science Foundation; Joan and Robert Arnow Chair of Theoretical Astrophysics |
Organisationseinheiten: | Mathematisch-Naturwissenschaftliche Fakultät / Institut für Physik und Astronomie |
Peer Review: | Referiert |