# Energy Spectra of Abundant Cosmic-ray Nuclei in Sources, According to the ATIC Experiment

## TL;DR

This paper analyzes the energy spectra of cosmic-ray nuclei from the ATIC experiment, back-propagates them to sources using diffusion models, and finds a statistically significant increase in spectral steepness with charge, consistent across models.

## Contribution

It introduces a method to reconstruct source spectra of cosmic-ray nuclei from ATIC data using GALPROP-based diffusion models, revealing a charge-dependent spectral steepening.

## Key findings

- Spectral indices in sources are weakly model dependent.
- Spectral steepness increases with charge from helium to iron.
- The increase in steepness is statistically significant at over 3 sigma.

## Abstract

One of the main results of the ATIC (Advanced Thin Ionization Calorimeter) experiment is a collection of energy spectra of abundant cosmic-ray nuclei: protons, He, C, O, Ne, Mg, Si, Fe measured in terms of energy per particle in the energy range from 50 GeV to tens of teraelectronvolts. In this paper, the ATIC energy spectra of abundant primary nuclei are back-propagated to the spectra in sources in terms of magnetic rigidity using a leaky-box approximation of three different GALPROP-based diffusion models of propagation that fit the latest B/C data of the AMS-02 experiment. It is shown that the results of a comparison of the slopes of the spectra in sources are weakly model dependent; therefore the differences of spectral indices are reliable data. A regular growth of the steepness of spectra in sources in the range of magnetic rigidity of 50--1350~GV is found for a charge range from helium to iron. This conclusion is statistically reliable with significance better than 3.2 standard deviations. The results are discussed and compared to the data of other modern experiments.