Monte Carlo Study of Electron and Positron Cosmic-Ray Propagation with the CALET Spectrum

TL;DR

This study uses Monte Carlo simulations to analyze how cosmic-ray electrons and positrons from supernova remnants contribute to the spectrum observed by CALET, revealing the impact of nearby sources and rare energetic events.

Contribution

It introduces a stochastic Monte Carlo approach to model cosmic-ray propagation, demonstrating that simple diffusion models can replicate observed spectra and suggesting rare, energetic supernova events influence the high-energy cosmic-ray flux.

Findings

Nearby supernovae contribute significantly to the TeV flux.

A rare, energetic supernova event explains the sharp spectral drop at 1 TeV.

Positron features are consistent with a bump around 300 GeV.

Abstract

Focusing on the electron and positron spectrum measured with CALET, which shows characteristic structures, we calculate flux contributions of cosmic rays escaped from supernova remnants, which were randomly born. We adopt a Monte Carlo method to take into account the stochastic property of births of nearby sources. We find that without a complicated energy dependence of the diffusion coefficient, simple power-law diffusion coefficients can produce spectra similar to the CALET spectrum even with a dispersion in the injection index. The positron component measured with AMS-02 is consistent with a bump-like structure around 300 GeV in the CALET spectrum. One to three nearby supernovae can contribute up to a few tens of percent of the CALET flux at 2--4 TeV, ten or more unknown and distant ($\gtrsim 500$ pc) supernovae account for the remaining several tens of percent of the flux. The CALET spectrum, showing a sharp drop at $\sim 1$ TeV, allows for a contribution of cosmic rays from an extraordinary event which occured $\sim 400$ kyr ago. This type of event releases electrons/positrons with a total energy more than 10 times the average energy for usual supernovae, and its occurrence rate is lower than $1/300$ of the usual supernova rate.