On the Origin of Cosmic Rays
arXiv:astro-ph/0111555
Abstract
The problem in identifying the sites of origin of Galactic Cosmic Rays (CRs) is reviewed. Recent observational evidence from very-high energy (VHE, energies above 100 GeV) gamma-ray measurements is in contradiction with the surmise that synchrotron radiation from relativistic electrons is indicative for hadron acceleration. It rather points to a CR-acceleration efficiency of supernova remnants (SNRs) below one percent, much less than the value required if these objects were to be the main sources of Galactic cosmic rays (about 30%). Observations of CR anisotropy and the emission of low-energy (energy < 10 GeV) gamma-rays from the Galactic disk indicate that the sources of low-energy cosmic rays are distributed with a Galactocentric radial scale length in the order of 25 +- 10 kpc, much larger than expected if SNRs are the main sources of CRs. These two facts - together with the body of evidence from CR isotope abundances - strongly suggest that a new class of astrophysical objects - distinct from SNRs and located manly in the outer reaches of our Galaxy - is the major source of hadronic CRs in our Galaxy. The basic observational features of ultra high-energy (UHE, energy > 10^{19} eV) CRs are most naturally understood if the same CR sources accelerate CRs up to the highest observed CR energies. Proposals for the nature of a new source class are mentioned. The origin of CRs is still as much shrouded in mystery as it was in 1957, when Philip Morrison wrote a seminal review about CR origin. The potential for discoveries is thus great.
27 pages, Latex, 5 eps figures
References in corpus (23)
- Propagation of cosmic-ray nucleons in the Galaxy
- Extension of the Cosmic-Ray Energy Spectrum Beyond the Predicted Greisen-Zatsepin-Kuz'min Cutoff
- On the acceleration of Ultra High Energy Cosmic Rays in Gamma Ray Bursts
- Discovery of TeV Gamma Rays from SN1006: Further Evidence for the SNR Origin of Cosmic Rays
- Radio to Gamma-Ray Emission from Shell-type Supernova Remnants: Predictions from Non-linear Shock Acceleration Models
- Cosmic Ray Protons and Magnetic Fields in Clusters of Galaxies and their Cosmological Consequences
- Detection of H-alpha emission from the Magellanic Stream: evidence for an extended gaseous Galactic halo
- Constraints on the Ultra High Energy Photon flux using inclined showers from the Haverah Park array
- The GZK Feature in our Neighborhood of the Universe
- Does MOND follow from the CDM paradigm?
- A search for possible interactions between ejections from GRS 1915+105 and the surrounding interstellar medium
- Supernovae, Pulsars and Gamma-Ray Bursts: A Unified Picture
- Origin of Cosmic Radiation
- Coronal Gamma Ray Bursts as the sources of Ultra High Energy Cosmic Rays?
- Tests of Galactic Cosmic Ray Source Models
- VHE Astronomy before the New Millenium
- Extragalactic ultra high energy cosmic rays, I. Contribution from hot spots in FR-II galaxies
- An extragalactic ``flux trapping'' origin of the dominant part of hadronic cosmic rays?
- Observations of the supernova remnant W28 at TeV energies
- Ultrahigh Energy Neutrinos and Cosmic Rays as Probes of New Physics
- Cosmic Rays and Gamma Ray Bursts From Microblazars
- A common origin of all the species of high-energy cosmic rays?
- Are Galactic Gamma-Ray Bursters the Main Source of Hadronic Non-Solar Cosmic Rays at all Energies?