Newly-Discovered Anomalies in Galactic Cosmic Rays: Time for Exotic Scenarios?

Malkov, Mikhail

doi:10.1016/j.nuclphysbps.2018.07.004

Cited by 6 publications

(3 citation statements)

References 62 publications

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“…These limit-cycle oscillations have been predicted from the analytic solution of the nonlinear acceleration problem. Indeed, they appear to be present in numerical solutions due to Kang & Jones (2002) (see their Fig.7 and a recent discussion of the phenomenon by Malkov 2018). As in the case of spatial variation of acceleration efficiency, the limit-cycle oscillations must result in a spectral index between its efficient and test-particle values.…”

Section: Acceleration Nonlinearity and Turbulent Heatingmentioning

confidence: 83%

Cosmic-ray Spectrum Steepening in Supernova Remnants. I. Loss-free Self-similar Solution

Malkov

Aharonian

2019

ApJ

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The direct measurements of cosmic rays (CRs), after correction for the propagation effects in the interstellar medium, indicate that their source spectra are likely to be significantly steeper than the canonical E −2 spectrum predicted by the standard Diffusive Shock Acceleration (DSA) mechanism. The DSA has long been held responsible for the production of galactic CRs in supernova remnant (SNR) shocks. The γ-ray "probes" of the acceleration spectra of CRs on-the-spot, inside of the SNRs, lead to the same conclusion. We show that the steep acceleration spectrum can be attributed to the combination of (i) spherical expansion, (ii) tilting of the magnetic field along the shock surface and (iii) shock deceleration. Because of (i) and (ii), the DSA is efficient only on two "polar caps" of a spherical shock where the local magnetic field is within 45 • to its normal. The shock-produced spectrum observed edge-on steepens with the particle energy because the number of freshly accelerated particles with lower energies continually adds up to a growing acceleration region. We demonstrate the steepening effect by obtaining an exact self-similar solution for the particle acceleration at expanding shock surface with an arbitrary energy dependence of particle diffusivity κ. We show that its increase toward higher energy steepens the spectrum, which deeply contrasts with the standard DSA spectrum where κ cancels out.

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Section: Acceleration Nonlinearity and Turbulent Heatingmentioning

confidence: 83%

Cosmic-ray Spectrum Steepening in Supernova Remnants. I. Loss-free Self-similar Solution

Malkov

Aharonian

2019

ApJ

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“…Resonantly driven by protons, it curbs them tighter downstream than heavier nuclei, so the latter may cross the shock to gain energy. As the above differentiation mechanism depends exclusively on á ñ A Q , its salient consequence is that all elements with the same á ñ A Q must have the same ultrarelativistic rigidity spectra (Malkov 2018). No exceptions to this rule have been reported so far (Aguilar et al 2021).…”

Section: Background Spectramentioning

confidence: 95%

On the Origin of Observed Cosmic-Ray Spectrum Below 100 TV

Malkov

Moskalenko²

2022

ApJ

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Recent precise measurements of primary and secondary cosmic-ray (CR) species in the teravolt rigidity domain have unveiled a bump in their spectra, located between 0.5 and 50 TV. We argue that a local shock may generate such a bump by increasing the rigidity of the preexisting CRs below 50 TV by a mere factor of ∼1.5. Reaccelerated particles below ∼0.5 TV are convected with the interstellar medium flow and do not reach the Sun, thus creating the bump. This single universal process is responsible for the observed spectra of all CR species in the rigidity range below 100 TV. We propose that one viable shock candidate is the Epsilon Eridani star at 3.2 pc from the Sun, which is well aligned with the direction of the local magnetic field. Other shocks, such as old supernova shells, may produce a similar effect. We provide a simple formula, Equation (9), that reproduces the spectra of all CR species with only two nonadjustable shock parameters, uniquely derived from the proton data. We show how our formalism predicts helium and carbon spectra and the B/C ratio.

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“…At least in one such case, the theory has already faced a serious challenge when a ∆q ≈ 0.1 difference between the proton and helium rigidity spectra was firmly established [2,3,4]. Explanations have been given (see [5,6] for a review), but only a few of them address the proton spectrum steepening relative to helium at the DSA level (see [7] and the references therein). These explanations do not vindicate the DSA ultimately because of the second type of disagreements associated with observations of individual particle spectra in SNRs.…”

Section: Introductionmentioning

confidence: 99%