Origin of Galactic Cosmic Rays

Abstract

The origin of the bulk of cosmic rays (CRs) observed at Earth is the topic of a century long investigation, paved with successes and failures. From the energetic point of view, supernova remnants (SNRs) remain the most plausible sources of CRs up to rigidity ? 10^6-10^7 GV. This confidence somehow resulted in the construction of a paradigm, the so-called SNR paradigm: CRs are accelerated through diffusive shock acceleration in SNRs and propagate diffusively in the Galaxy in an energy dependent way. Qualitative confirmation of the SNR acceleration scenario has recently been provided by gamma ray and X-ray observations. Diffusive propagation in the Galaxy is probed observationally through measurement of the secondary to primary nuclei flux ratios (such as B/C). There are however some weak points in the paradigm, which suggest that we are probably missing some physical ingredients in our models. The theory of diffusive shock acceleration at SNR shocks predicts spectra of accelerated particles which are systematically too hard compared with the ones inferred from gamma ray observations. Moreover, hard injection spectra indirectly imply a steep energy dependence of the diffusion coefficient in the Galaxy, which in turn leads to anisotropy larger than the observed one. Moreover recent measurements of the flux of nuclei suggest that the spectra have a break at rigidity ? 200 GV, which does not sit well with the common wisdom in acceleration and propagation. In this paper I will review these new developments and suggest some possible implications.

Invited Review Talk in SciNeGHE 2012, 20-22 June 2012, Lecce (Italy)

References in corpus (14)

• Discrepant hardening observed in cosmic-ray elemental spectra
• Spectral breaks as a signature of cosmic ray induced turbulence in the Galaxy
• A kinetic approach to cosmic ray induced streaming instability at supernova shocks
• Non linear particle acceleration at non-relativistic shock waves in the presence of self-generated turbulence
• Measuring the cosmic ray acceleration efficiency of a supernova remnant
• Spectrum of cosmic rays, produced in supernova remnants
• A dip in the UHECR spectrum and the transition from galactic to extragalactic cosmic rays
• Dynamical Feedback of Self-generated Magnetic Fields in Cosmic Ray Modified Shocks
• Cosmic-ray acceleration in supernova remnants: non-linear theory revised
• The maximum momentum of particles accelerated at cosmic ray modified shocks
• Dynamical effects of self-generated magnetic fields in cosmic ray modified shocks
• Turbulence Dissipation and Particle Injection in Non-Linear Diffusive Shock Acceleration with Magnetic Field Amplification
• Non-linear diffusive acceleration of heavy nuclei in supernova remnant shocks
• Signatures of the transition from galactic to extragalactic cosmic rays

Cited by in corpus (6)

• Search for Extended Sources of Neutrino Emission in the Galactic Plane with IceCube
• Possible contribution of X-ray binary jets to the Galactic cosmic ray and neutrino flux
• The prototype X-ray binary GX 339-4: using TeV gamma-rays to assess LMXBs as Galactic cosmic ray accelerators
• Ultrarelativistic generalized Lorentzian thermodynamics and the differential cosmic ray energy flux
• A tale of cosmic rays narrated in gamma rays by Fermi
• Determination of the mass and energy of primary cosmic rays above 100 TeV