Erratum: Signature of Energy Losses on the Cosmic Ray Electron Spectrum [Phys. Rev. Lett. 125, 051101 (2020)].

This corrects the article DOI: 10.1103/PhysRevLett.125.051101.

Signature of Energy Losses on the Cosmic Ray Electron Spectrum.

We show that the fine structure of the electron spectrum in cosmic rays, especially the excess claimed by AMS-02 at energies ≳42 GeV, is fully accounted for in terms of inverse Compton losses in the photon background dominated by ultraviolet, infrared, and cosmic microwave background photons, plus the standard synchrotron losses in the Galactic magnetic field. The transition to the Klein-Nishina regime on the ultraviolet background causes the feature. Hence, contrary to previous statements, observations do not require the overlap of different components. We stress that the feature observed by AMS-02 at energies ≳42 GeV is not related to the positron excess, which instead requires the existence of positron sources, such as pulsars. Because energy losses are the physical explanation of this feature, we indirectly confirm that the transport of leptons in the Galaxy is loss dominated down to energies of the order of tens of GeV. This finding imposes strong constraints on the feasibility of alternative theories of cosmic transport in which the grammage is accumulated in cocoons concentrated around sources, requiring that electrons and positrons become loss dominated only at very high energies.

Origin of the Cosmic Ray Galactic Halo Driven by Advected Turbulence and Self-Generated Waves.

The diffusive paradigm for the transport of Galactic cosmic rays is central to our understanding of the origin of these high energy particles. However, it is worth recalling that the normalization, energy dependence, and spatial extent of the diffusion coefficient in the interstellar medium are fitted to the data and typically are not derived from more basic principles. Here, we discuss a scenario in which the diffusion properties of cosmic rays are derived from a combination of wave self-generation and advection from the Galactic disc, where the sources of cosmic rays are assumed to be located. We show for the first time that a halo naturally arises from these phenomena, with a size of a few kiloparsecs, compatible with the value that typically best fits observations in simple parametric approaches to cosmic ray diffusion. We also show that transport in such a halo results in a hardening in the spectra of primary cosmic rays at ∼300 GV.

Three-dimensional model of cosmic-ray lepton propagation reproduces data from the Alpha Magnetic Spectrometer on the International Space Station.

We study the compatibility of Alpha Magnetic Spectrometer (AMS-02) data on the cosmic-ray (CR) positron fraction with data on the CR electron and positron spectra provided by PAMELA and Fermi LAT. We do that in terms of a novel propagation model in which sources are distributed in spiral arm patterns in agreement with astrophysical observations. While former interpretations assumed an unrealistically steep injection spectrum for astrophysical background electrons, the enhanced energy losses experienced by CR leptons due to the larger average source distance from Earth allow us to reproduce the data with harder injection spectra as expected in a shock acceleration scenario. Moreover, we show that in this approach, and accounting for AMS-02 results, the contribution of nearby accelerators to the fluxes at very high energy can be significantly reduced, thus avoiding any tension with anisotropy upper limits.

Common solution to the cosmic ray anisotropy and gradient problems.

Multichannel cosmic ray spectra and the large scale cosmic ray anisotropy can hardly be made compatible in the framework of conventional isotropic and homogeneous propagation models. These models also have problems explaining the longitude distribution and the radial emissivity gradient of the γ-ray Galactic interstellar emission. We argue here that accounting for a physically motivated correlation between the cosmic ray escape time and the spatially dependent magnetic turbulence power can naturally solve both problems. Indeed, by exploiting this correlation we find propagation models that fit a wide set of cosmic ray spectra, and consistently reproduce the cosmic ray anisotropy in the energy range 10(2)-10(4) GeV and the γ-ray longitude distribution recently measured by Fermi-LAT.