ORIGIN OF ULTRA-HIGH-ENERGY GALACTIC COSMIC RAYS: THE ISOTROPY PROBLEM

Journal Article · Thu Dec 01 04:00:00 EST 2011 · Astrophysical Journal

DOI:https://doi.org/10.1088/0004-637X/742/2/114· OSTI ID:22004586

Pohl, Martin ^[1]; Eichler, David ^[2]

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1. Institut fuer Physik und Astronomie, Universitaet Potsdam, 14476 Potsdam-Golm (Germany)
2. Physics Department, Ben-Gurion University, Be'er-Sheva 84105 (Israel)

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{sup 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{sup 18} eV.

• OSTI ID: 22004586
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 742; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ANALYTICAL SOLUTION
ANISOTROPY
BARYONS
COSMIC GAMMA BURSTS
EEV RANGE
GALACTIC EVOLUTION
GALAXIES
ISOTROPY
MEAN FREE PATH
MONTE CARLO METHOD
RANDOMNESS
STARS
TIME DEPENDENCE