Cosmic-ray acceleration in supernova remnants: non-linear theory revised

By D. Caprioli. 2012

133 citations recorded by the source corpus.

A rapidly growing amount of evidences, mostly coming from the recent gamma-ray observations of Galactic supernova remnants (SNRs), is seriously challenging our understanding of how particles are accelerated at fast shocks. The cosmic-ray (CR) spectra required to account for the observed phenomenology are in fact as steep as E−2.2–E−2.4, i.e., steeper than the test-particle prediction of first-order Fermi acceleration, and significantly steeper than what expected in a more refined non-linear theory of diffusive shock acceleration. By accounting for the dynamical back-reaction of the non-thermal particles, such a theory in fact predicts that the more efficient the particle acceleration, the flatter the CR spectrum. In this work we put forward a self-consistent scenario in which the account for the magnetic field amplification induced by CR streaming produces the conditions for reversing such a trend, allowing — at the same time — for rather steep spectra and CR acceleration efficiencies (about 20%) consistent with the hypothesis that SNRs are the sources of Galactic CRs. In particular, we quantitatively work out the details of instantaneous and cumulative CR spectra during the evolution of a typical SNR, also stressing the implications of the observed levels of magnetization on both the expected maximum energy and the predicted CR acceleration efficiency. The latter naturally turns out to saturate around 10-30%, almost independently of the fraction of particles injected into the acceleration process as long as this fraction is larger than about 10−4.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/3c232978b7083b3fcca87c89c23292aac4d9be24

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In Astronomy and Astrophysics

1. A. Spitkovsky
2. D. Caprioli
3. M. Unger
4. R. Ulrich
5. K. Kampert
6. L. Sironi
7. J. Arons
8. D. Giannios

In Nuclear and High Energy Physics

1. A. Spitkovsky
2. D. Caprioli
3. M. Unger
4. A. Fedynitch
5. R. Ulrich
6. K. Kampert
7. L. Cazon
8. W. Rhode

Citations in the corpus

• SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. II. MAGNETIC FIELD AMPLIFICATION (2014, background): “PIC simulations in periodic boxes showed that the Alfvén velocity grows proportionally to the magnetic field in the nonlinear stage of the instability (Riquelme & Spitkovsky 2009), and the enhanced phase velocity of selfgenerated modes may play an important role in explaining the steep ion spectra ”
• SIMULATIONS OF ION ACCELERATION AT NON-RELATIVISTIC SHOCKS. I. ACCELERATION EFFICIENCY (2013, methodology): “However, concave spectra, flatter than p−4 at the highest energies, have never been convincingly observed in SNRs, even when CR acceleration is inferred to be efficient (Caprioli 2012).”
• The origin of galactic cosmic rays (2013, unknown): “Several authors (Ptuskin et al. 2010; Caprioli et al. 2010a; Caprioli 2012) suggested that appreciably steeper spectra may be obtained by assuming fast moving scattering centers in the upstream fluid, but this effect appears to be dependent on rather poorly known characteristics of the waves…”
• The Muon Puzzle in cosmic-ray induced air showers and its connection to the Large Hadron Collider (2021, background): “Cosmic rays with energies below 1 PeV = 106 GeV are commonly assumed to be produced by shock acceleration in super-nova remnants (Blasi 2011; Caprioli 2012).”