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The theory of non-linear diffusive shock acceleration (NLDSA) predicts the formation of a precursor upstream of the shock, where accelerated particles diffuse and induce magnetic field amplification (MFA) through streaming instability. The non-detection of this precursor in X-rays in Chandra observations of the north-eastern region of SN 1006 (G329.6+14.6) led the authors of some previous work to impose an upper limit to the X-ray emission generated by accelerated electrons diffusing in this precursor, at an emissivity level of <1.5 per cent of the emission from the downstream region. This has been used as an argument against Fermi acceleration at this shock. Here, we calculate the spectrum and spatial distribution of accelerated particles in SN 1006 and show that Chandra results (including more recent data) are in perfect agreement with the predictions of NLDSA suggesting efficient particle acceleration and MFA upstream of the shock by a factor of ∼10. [ABSTRACT FROM AUTHOR]

We calculate the flux of non-thermal radiations from the supernova remnant (SNR) RX J1713.7−3946 in the context of the non-linear theory of particle acceleration at shocks, which allows us to take into account self-consistently the dynamical reaction of the accelerated particles, the generation of magnetic fields in the shock proximity and the dynamical reaction of the magnetic field on the plasma. When the fraction of particles which get accelerated is of the order of ∼10−4, we find that the strength of the magnetic field obtained as a result of streaming instability induced by cosmic rays is compatible with the interpretation of the X-ray emitting filaments being produced by strong synchrotron losses in G magnetic fields. The maximum energy of accelerated protons is GeV. If the X-ray filaments are explained in alternative ways, the constraint on the magnetic field downstream of the shock disappears and the HESS data can be marginally fitted with ICS of relativistic electrons off a complex population of photons, tailored to comprise cosmic microwave background and ambient infrared/optical photons. The fit, typically poor at the highest energies, requires a large density of target photons within the remnant; only a fraction of the order of ∼10−6 of the background particles gets accelerated; the local magnetic field is of the order of G and the maximum energy of protons is much lower than the knee energy. Current HESS gamma-ray observations combined with recent X-ray observations by Suzaku do not allow as yet to draw a definitive conclusion on whether RX J1713.7−3946 is an efficient cosmic ray accelerator, although at the present time a hadronic interpretation of HESS data seems more likely. We discuss the implications of our results for the GLAST gamma-ray telescope, which should be able to discriminate the two scenarios discussed above, by observing the shape of the gamma-ray spectrum at lower energies. [ABSTRACT FROM AUTHOR]

Stationary solutions to the problem of particle acceleration at shock waves in the non-linear regime, when the dynamical reaction of the accelerated particles on the shock cannot be neglected, are known to show a prominent energy flux escaping from the shock towards upstream infinity. On physical grounds, the escape of particles from the upstream region of a shock has to be expected in all those situations in which the maximum momentum of accelerated particles, , decreases with time, as is the case for the Sedov–Taylor phase of expansion of a shell supernova remnant, when both the shock velocity and the cosmic ray induced magnetization decrease. In this situation, at each time t, particles with momenta larger than leave the system from upstream, carrying away a large fraction of the energy if the shock is strongly modified by the presence of cosmic rays. This phenomenon is of crucial importance for explaining the cosmic ray spectrum detected at the Earth. In this paper, we discuss how this escape flux appears in the different approaches to non-linear diffusive shock acceleration, and especially in the quasi-stationary semi-analytical kinetic ones. We apply our calculations to the Sedov–Taylor phase of a typical supernova remnant, including in a self-consistent way particle acceleration, magnetic field amplification and the dynamical reaction on the shock structure of both particles and fields. Within this framework, we calculate the temporal evolution of the maximum energy reached by the accelerated particles and of the escape flux towards upstream infinity. The latter quantity is directly related to the cosmic ray spectrum detected at the Earth. [ABSTRACT FROM AUTHOR]