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Theoretical interpretation of Pass 8 Fermi-LAT $e^+$ + $e^-$ dataAnomalies in Cosmic Ray Composition: Explanation Based on Mass to Charge Ratio

A. Hanusch, T. Liseykina, M. Malkov

in 35th International Cosmic Ray Conference

Contribution: pdf


High precision spectrometry of galactic cosmic rays (CR) has revealed
the lack of our understanding of how different CR elements are extracted from
the supernova environments to be further accelerated in their shocks. Comparing
the spectra of accelerated particles with different mass to charge ratios is a
powerful tool for studying the physics of particle injection into the diffusive
shock acceleration (DSA). Recent AMS-02 demonstration of the similarity of He/$p$,
C/$p$, and O/$p$ rigidity spectra has provided new evidence that injection is a
mass-to-charge dependent process. We performed hybrid simulations of collisionless
shocks and analyzed a joint injection of $p$ and He$^{2+}$ in conjunction with
upstream waves they generate. By implication, our results equally apply to C and O
fully ionized ions, since they have similar mass to charge ratios. By convolving
the time-dependent injection rates of $p$ and He, obtained from the simulations,
with a decreasing shock strength over the active life of SNRs, we generate the
integrated SNR spectra for $p$ and He. These spectra are consistent with the AMS-02
and Pamela data and earlier theoretical predictions. Our interpretation of the
elemental anomaly is therefore intrinsic to collisionless shock mechanisms and does
not require additional assumptions, such as the contributions from several different
SNRs, their inhomogeneous environments or acceleration from grains.