On the mechanism for breaks in the cosmic ray spectrum

Abstract

The proof of cosmic ray (CR) origin in supernova remnants (SNR) must hinge on full consistency of the CR acceleration theory with the observations; direct proof is impossible because of the orbit stochasticity of CR particles. Recent observations of a number of galactic SNR strongly support the SNR-CR connection in general and the Fermi mechanism of CR acceleration, in particular. However, many SNR expand into weakly ionized dense gases, and so a significant revision of the mechanism is required to fit the data. We argue that strong ion-neutral collisions in the remnant surrounding lead to the steepening of the energy spectrum of accelerated particles by \emph{exactly one power}. The spectral break is caused by a partial evanescence of Alfven waves that confine particles to the accelerator. The gamma-ray spectrum generated in collisions of the accelerated protons with the ambient gas is also calculated. Using the recent Fermi spacecraft observation of the SNR W44 as an example, we demonstrate that the parent proton spectrum is a classical test particle power law $\propto E^{-2}$, steepening to $E^{-3}$ at $E_{br}\approx 7GeV$.

APS talk to appear in PoP, 4 figures

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• Cosmic-ray acceleration and escape from post-adiabatic Supernova remnants
• The supernova remnant W49B as seen with H.E.S.S. and Fermi-LAT
• Acceleration of cosmic rays by young core-collapse supernova remnants
• Fermi-LAT Observations of Supernova Remnant Kesteven 79
• H.E.S.S. detection of TeV emission from the interaction region between the supernova remnant G349.7+0.2 and a molecular cloud
• H.E.S.S. reveals a lack of TeV emission from the supernova remnant Puppis A
• Plus Charge Prevalence in Cosmic Rays: Room for Dark Matter in the Positron Spectrum
• The high-energy gamma-ray detection of G73.9+0.9, a supernova remnant interacting with a molecular cloud
• Multi-wavelength analysis of the Galactic supernova remnant MSH 11-61A
• Cosmic Ray Confinement and Transport Models for Probing their Putative Sources