The role of ionization in the shock acceleration theory

Abstract

We study the acceleration of heavy nuclei at SNR shocks taking into account the process of ionization. In the interstellar medium atoms heavier then hydrogen which start the diffusive shock acceleration (DSA) are never fully ionized at the moment of injection. We will show that electrons in the atomic shells are stripped during the acceleration process, when the atoms already move relativistically. For typical environment around SNRs the dominant ionization process is the photo-ionization due to the background galactic radiation. The ionization has two interesting consequences. First, because the total photo-ionization time is comparable to the beginning of the Sedov-Taylor phase, the maximum energy which ions can achieve is smaller than the standard result of the DSA, which predict $E_{\max }\propto Z_N$. As a consequence the structure of the CR spectrum in the {\it knee} region can be affected. The second consequence is that electrons are stripped from atoms when they already move relativistically hence they can start the DSA without any pre-acceleration mechanism. We use the linear quasi-stationary approach to compute the spectrum of ions and electrons accelerated after being stripped. We show that the number of these secondary electrons is enough to account for the synchrotron radiation observed from young SNRs, if the amplification of the magnetic field occurs.

Revised version (Added references, corrected typos, results unchanged) 13 pages, 7 figures. Accepted for publication in MNRAS 2010 November 22. Received 2010 October 22

References in corpus (9)

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• Gamma ray emission from SNR RX J1713.7-3946 and the origin of galactic cosmic rays
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• Electron Shock Surfing Acceleration in Multidimensions: Two-dimensional Particle-In-Cell Simulation of Collisionless Perpendicular Shock
• Non-linear diffusive acceleration of heavy nuclei in supernova remnant shocks
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Cited by in corpus (8)

• Diffusive propagation of cosmic rays from supernova remnants in the Galaxy. I: spectrum and chemical composition
• Origin of Cosmic Rays
• Numerical simulations of diffusive shock acceleration in SNRs
• Particle acceleration by supernova shocks and spallogenic nucleosynthesis of light elements
• Secondary Cosmic Ray Nuclei from Supernova Remnants and Constraints to the Propagation Parameters
• Radioactivity and Electron Acceleration in Supernova Remnants
• Possible physics scenarios behind cosmic-ray "anomalies"
• Role of the radiative stage for cosmic ray acceleration in SNRs