Non‐linear particle acceleration at non‐relativistic shock waves in the presence of self‐generated turbulence

INAF – Osservatorio Astrofisico di Arcetri, Largo E. Fermi, 5, 50125, Firenze, Italy
Monthly Notices of the Royal Astronomical Society (Impact Factor: 5.11). 09/2006; 371(3):1251 - 1258. DOI: 10.1111/j.1365-2966.2006.10739.x


Particle acceleration at astrophysical shocks may be very efficient if magnetic scattering is self-generated by the same particles. This non-linear process adds to the non-linear modification of the shock due to the dynamical reaction of the accelerated particles on the shock. Building on a previous general solution of the problem of particle acceleration with arbitrary diffusion coefficients, we present here the first semi-analytical calculation of particle acceleration with both effects taken into account at the same time; charged particles are accelerated in the background of Alfvén waves that they generate due to the streaming instability, and modify the dynamics of the plasma in the shock vicinity.

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    • "This idea is motivated by cosmicray source candidates like pulsars and supernova remnants being rather young (see, e.g. [39] [17] [25] [14]) and therefore mostly confined to the vicinity of the star-formation regions and thus to the vicinity of the spiral arms. Just recently, supernova remnants (SNRs) have received observational support as sources of cosmic rays (see [2]), supporting the link between cosmic-ray sources candidates and star-forming regions. "
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    ABSTRACT: We study the impact of possible spiral-arm distributions of Galactic cosmic-ray sources on the flux of various cosmic-ray nuclei throughout our Galaxy. We investigate model cosmic-ray spectra at the nominal position of the sun and at different positions within the Galaxy. The modelling is performed using the recently introduced numerical cosmic ray propagation code Picard. Assuming non-axisymmetric cosmic ray source distributions yields new insights on the behaviour of primary versus secondary nuclei.
    Astroparticle Physics 04/2015; 70. DOI:10.1016/j.astropartphys.2015.04.003 · 3.58 Impact Factor
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    • "Direct numerical simulations of the CR-modified shock by particlein-cell technique are nonfeasible by now because of the wide dynamical range of the simulation that requires extreme computing resources. Nevertheless, an approximate iterative approach (e.g., within the Monte Carlo model discussed in Vladimirov et al. (2008) or semi-analytical kinetic models developed by Malkov (1997); Amato and Blasi (2006)) can be used to derive the steady-state distribution function consistent with the shock compression. These approximate models assume some diffusion model and parameterize the microphysical processes of magnetic field amplification and plasma heating. "
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    ABSTRACT: In this review we discuss some observational aspects and theoretical models of astrophysical collisionless shocks in partly ionized plasma with the presence of non-thermal components. A specific feature of fast strong collisionless shocks is their ability to accelerate energetic particles that can modify the shock upstream flow and form the shock precursors. We discuss the effects of energetic particle acceleration and associated magnetic field amplification and decay in the extended shock precursors on the line and continuum multi-wavelength emission spectra of the shocks. Both Balmer-type and radiative astrophysical shocks are discussed in connection to supernova remnants interacting with partially neutral clouds. Quantitative models described in the review predict a number of observable line-like emission features that can be used to reveal the physical state of the matter in the shock precursors and the character of nonthermal processes in the shocks. Implications of recent progress of gamma-ray observations of supernova remnants in molecular clouds are highlighted.
    Space Science Reviews 05/2013; 178(2-4). DOI:10.1007/s11214-013-9984-7 · 6.28 Impact Factor
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    • "The case of Tycho is instructive as an illustration of the level of credibility of calculations based on the theory of NLDSA: the different techniques agree fairly well (see (Caprioli et al, 2010) for a discussion of this point) as long as only the dynamical reaction of accelerated particles on the shock is included. When magnetic effects are taken into account, the situation becomes more complex: in the calculations based on the semi-analytical description of Amato and Blasi (2006) the field is estimated from the growth rate and the dynamical reaction of the magnetic field on the shock is taken into account (Caprioli et al, 2008, 2009b). Similar assumptions are adopted by Vladimirov et al (2008), although the technique is profoundly different. "
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    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 di?usive shock acceleration in SNRs and propagate di?ffusively 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. Diff?usive 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 diff?usive 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.
    Nuclear Physics B - Proceedings Supplements 11/2012; s 239–240(1). DOI:10.1016/j.nuclphysbps.2013.05.023 · 0.88 Impact Factor
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