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

Katsuaki Asano,Toshio Terasawa,Yoichi Asaoka,Norita Kawanaka,Yosui Akaike,Holger M Motz,Kazunori Kohri

doi:10.3847/1538-4357/ac41d1

Abstract

Abstract Focusing on the electron and positron spectrum measured with the Calorimetric Electron Telescope (CALET), which shows characteristic structures, we calculate the flux contributions of cosmic rays that have escaped from randomly appearing supernova remnants. We adopt a Monte Carlo method to take into account the stochastic nature of the appearance 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, while ten or more unknown and distant (≳500 pc) supernovae account for the remaining several tens of percent of the flux. The CALET spectrum, showing a sharp drop at ∼1 TeV, allows for a contribution of cosmic rays from an extraordinary event that occurred ∼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 one three-hundredth of the usual supernova rate.

Highlights

Direct measurements of electron and positron cosmic-rays (CRs) have been pioneered by various teams such as BETS (Torii et al 2001), HEAT (DuVernois et al 2001), ATIC (Chang et al 2008), PPB-BETS (Yoshida et al 2008), and PAMELA (Adriani et al 2011)
While the spectra of electron and positron CRs measured with AMS-02 and CALET are consistent, the spectra obtained with Fermi-LAT and DAMPE show slightly harder shape and higher fluxes above 300 GeV
When accidentally a few recent and nearby sources occur in a sample, the flux above ∼ TeV becomes significantly larger than the CALET flux

Summary

Introduction

Direct measurements of electron and positron cosmic-rays (CRs) have been pioneered by various teams such as BETS (Torii et al 2001), HEAT (DuVernois et al 2001), ATIC (Chang et al 2008), PPB-BETS (Yoshida et al 2008), and PAMELA (Adriani et al 2011). The electron and positron CR study (total CR flux not distinguishing their charge signs) has been greatly advanced with new instruments such as AMS-02 (Aguilar et al 2014, 2019), Fermi-LAT (Abdollahi et al 2017), CALET (Adriani et al 2017, 2018; Torii & Akaike 2021), and DAMPE (Ambrosi et al 2017). While the spectra of electron and positron CRs measured with AMS-02 and CALET are consistent, the spectra obtained with Fermi-LAT and DAMPE show slightly harder shape and higher fluxes above 300 GeV. The small number of nearby sources implies a large dispersion in the predicted TeV flux as discussed in Kawanaka et al (2010); Cholis et al (2018); Fang et al (2018); Mertsch (2018)

Methods

Results

Conclusion