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PAMELA and AMS-02 positron and electron spectra are reproduced by three-dimensional cosmic-ray modeling

Journal article
Authors Gaggero Daniele
Maccione Luca
Giuseppe Di Bernardo
Grasso Dario
Evoli Carmelo
Published in Physical Review D. Particles and fields
Volume D89
Pages 083007
ISSN 0556-2821
Publication year 2014
Published at Department of Physics (GU)
Pages 083007
Language en
Subject categories High energy astrophysics


The PAMELA collaboration recently released the e+ absolute spectrum between 1 and 300 GeV in addition to the positron fraction and the e− spectrum previously measured in the same period. We use the newly developed three-dimensional upgrade of the dragon package to model those data. This code allows us to consider a realistic spiral-arm source distribution in the Galaxy, which impacts the high-energy shape of the propagated spectra. At low energy we treat solar modulation with the HelioProp code and compare its results with those obtained using the usual force-field approximation. We show that all PAMELA data sets can be consistently, and accurately, described in terms of a standard background on top of which a charge symmetric e++e− extra component with harder injection spectrum is added; this extra contribution is peaked at ∼1–10  TeV and may originate from a diffuse population of sources located in the Galactic arms. For the first time, we compute the energy required to sustain such a relevant positron flux in the Galaxy, finding that it is naturally compatible with an astrophysical origin. We considered several reference propagation setups; we find that models with a low (or null) reacceleration—tuned against light nuclei data—nicely describe both PAMELA leptonic and hadronic data with no need to introduce a low-energy break in the proton and Helium spectra, as it would be required for high reacceleration models. We also compare our models with the preliminary e− and e+ absolute spectra recently measured by AMS-02. We find that those data, differently from what is inferred from the positron fraction alone, favor a high energy cutoff ∼10  TeV of the extra component if this is uniquely generated in the Galactic arms. A lower cutoff may be allowed if a relevant contribution from powerful e−+e+ nearby accelerators (e.g., one or few pulsars) is invoked.

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