c ∗

• Main Authors: Thomas J. Weiler, Thomas W. Kephart
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 1996
• Subjects: of the Fly’s Eye event. In addition; the mean; Yakutsk
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.257.8801; http://arxiv.org/pdf/astro-ph/9605156v1.pdf

We suggest that the highest energy> ∼ 10 20 eV cosmic ray primaries may be relativistic magnetic monopoles. Motivations for this hypothesis are twofold: (i) conventional primaries are problematic, while monopoles are naturally accelerated to E ∼ 10 20 eV by galactic magnetic fields; (ii) the observed highest energy cosmic ray flux is just below the Parker limit for monopoles. By matching the cosmic monopole production mechanism to the observed highest energy cosmic ray flux we estimate the monopole mass to be < ∼ 10 10 GeV. The recent discoveries by the AGASA [1], Fly’s Eye [2], Haverah Park [3], and Yakutsk [4] collaborations of cosmic rays with energies above the GZK [5] cut–off at Ec ∼ 5 × 10 19 eV present an intriguing challenge to particle astrophysics. The origin of the cut–off is degradation of the proton energy by resonant scattering on the 3K cosmic background radiation; above threshold, a ∆ ∗ is produced which then decays to nucleon plus pion. For every mean free path ∼ 6 Mpc of travel, the proton loses 20 % of its energy on average. So if protons are the primaries for the highest energy cosmic rays they must either come from a rather nearby source ( < ∼ 50 to 100 Mpc [6]) or have an initial energy far above 10 20 eV. Neither possibility seems likely, although the suggestion has been made that radio galaxies at distances 10 to 200 h −1 100 Mpc in the supergalactic plane may be origins [7]. A primary nucleus mitigates the cut–off problem (energy per nucleon is reduced by 1/A), but has additional problems: above ∼ 1019 eV nuclei should be photo–dissociated by the 3K background [8], and possibly disintegrated by the particle density ambient at the astrophysical source. Gamma–rays and neutrinos are other possible primary candidates for these highest energy events. However, the gamma–ray hypothesis appears inconsistent [9] with the time–development