Solicited review article prepared for Reports on Progress in Physics (2004)
astro-ph/0402371

For a PDF version of the article, click here.
Report-no: NUB-3244/Th-04


ASTROPHYSICAL ORIGINS OF ULTRAHIGH ENERGY COSMIC RAYS

Diego F. Torres a and Luis A. Anchordoqui b

a Lawrence Livermore National Laboratory, 7000 East Ave., L-413,
Livermore, CA 94550, USA

b Department of Physics, Northeastern University
Boston, MA 02115, USA

dtorres@igpp.ucllnl.org
l.anchordoqui@neu.edu


Abstract. In the first part of this review we discuss the basic observational features at the end of the cosmic ray energy spectrum. We also present there the main characteristics of each of the experiments involved in the detection of these particles. We then briefly discuss the status of the chemical composition and the distribution of arrival directions of cosmic rays. After that, we examine the energy losses during propagation, introducing the Greisen-Zaptsepin-Kuzmin (GZK) cutoff, and discuss the level of confidence with which each experiment have detected particles beyond the GZK energy limit. In the second part of the review, we discuss astrophysical environments able to accelerate particles up to such high energies, including active galactic nuclei, large scale galactic wind termination shocks, relativistic jets and hot-spots of Fanaroff-Riley radiogalaxies, pulsars, magnetars, quasar remnants, starbursts, colliding galaxies, and gamma ray burst fireballs. In the third part of the review we provide a brief summary of scenarios which try to explain the super-GZK events with the help of new physics beyond the standard model. In the last section, we give an overview on neutrino telescopes and existing limits on the energy spectrum and discuss some of the prospects for a new (multi-particle) astronomy. Finally, we outline how extraterrestrial neutrino fluxes can be used to probe new physics beyond the electroweak scale.


PREFACE

Reviewing cosmic ray physics is a risky business. Theoretical models continue to appear at an amazing rate, both in the astrophysical and more exotic domains. We warn the reader: we do not (nor we could) intend to make an homogeneous coverage of all the ideas of our fellow colleagues. Reading differently focused reviews on the issue (quoted here along the way) is, in our view, the best approach to such a wide topic of research.


Table of Contents

THERE'S SOMETHING ABOUT COSMIC RAY OBSERVATIONS
Experiments and future projects
Primary species
Distribution of arrival directions
Propagation of UHECRs
GZK-end of the cosmic ray spectrum?

VANILLA SKY: UHECR GENERATION WITHIN THE STANDARD LORE
A brief low energy perspective
Plausible sources of UHECRs and the Hillas' plot
Neutron stars
Radio Galaxies and Active Galactic Nuclei
Remnants of quasars
Starbursts
Luminous Infrared Galaxies
Gamma-ray bursts

FULL THROTTLE: UHECR GENERATION BEYOND THE STANDARD LORE
Minority Report: Neutrino Showers
Bounds on the energy spectrum
Astronomy on Ice
Probes of new physics beyond the electroweak scale

ANY GIVEN SUNDAY: COUNTDOWN TO DISCOVERY

REFERENCES

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