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Supernova remnants (SNRs), as the major contributors to the galactic cosmic rays (CRs), are believed to maintain an average CR spectrum by diffusive shock acceleration regardless of the way they release CRs into the interstellar medium (ISM). However, the interaction of the CRs with nearby gas clouds crucially depends on the release mechanism. We call into question two aspects of a popular paradigm of the CR injection into the ISM, according to which they passively and isotropically diffuse in the prescribed magnetic fluctuations as test particles. First, we treat the escaping CR and the Alfvén waves excited by them on an equal footing. Second, we adopt field-aligned CR escape outside the source, where the waves become weak. An exact analytic self-similar solution for a CR "cloud" released by a dimmed accelerator strongly deviates from the test-particle result. The normalized CR partial pressure may be approximated as P(p, z, t ) = 2[∣z∣5/3 + z 5/3 dif exp[-z-3/5 exp[-z2(p)t ], where p is the momentum of CR particle, and z is directed along the field. The core of the cloud expands as zISM(p)t ], where p is the momentum of CR particle, and z is directed along the field. The core of the cloud expands as zdif α √DNL (p) t and decays in time as P α 2z-1 dif (t ). The diffusion coefficient DNL is strongly suppressed compared to its background ISM value DISM: DNL for sufficiently high field-line-integrated CR partial pressure, Π. When Π ⪢ 1, the CRs drive Alfvén waves efficiently enough to build a transport barrier (P ≈ 2/ ∣z∣-"pedestal") that strongly reduces the leakage. The solution has a spectral break at p = pISM exp (-Π) ⪡ DISM for sufficiently high field-line-integrated CR partial pressure, Π. When Π ⪢ 1, the CRs drive Alfvén waves efficiently enough to build a transport barrier (P ≈ 2/ ∣z∣-"pedestal") that strongly reduces the leakage. The solution has a spectral break at p = pbr, where pbr) ≃z²/t. [ABSTRACT FROM AUTHOR]NL (pbr) ≃z²/t. [ABSTRACT FROM AUTHOR]

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 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 ∝E-2, steepening to E-3 at Ebr≈7 GeV. [ABSTRACT FROM AUTHOR]

The much-anticipated proof of cosmic ray (CR) acceleration in supernova remnants must hinge on the full consistency of acceleration theory with the observations; direct proof is impossible because of CR-orbit scrambling. Recent observations indicate deviations between helium and proton CR rigidity spectra inconsistent with the theory. By considering an initial (injection) phase of the diffusive shock acceleration, where elemental similarity does not apply, we demonstrate that the spectral difference is, in fact, a unique signature of the acceleration mechanism. Collisionless shocks inject more He2+ when they are stronger and so produce harder He2+ spectra. The injection bias is due to Alfvén waves driven by the more abundant protons, so the He2+ ions are harder to trap by these waves. By fitting the p/He ratio to the PAMELA data, we bolster the diffusive shock acceleration case for resolving the century-old mystery of CR origin. [ABSTRACT FROM AUTHOR]