Excesses of Cosmic Ray Spectra from A Single Nearby Source

TL;DR

This paper proposes that a nearby supernova remnant near a molecular cloud can explain the observed universal excesses in cosmic ray spectra, including primary and secondary particles, and their anisotropies.

Contribution

It introduces a model where a single local supernova remnant accounts for cosmic ray excesses and anisotropies, differing from the traditional background source ensemble.

Findings

The local supernova remnant can produce harder spectra consistent with observations.

Secondary cosmic rays are generated through interactions with molecular gas, explaining excesses.

Proton anisotropy aligns with observations if the source is young and located at the anti-Galactic center.

Abstract

Growing evidence reveals universal hardening on various cosmic ray spectra, e.g. proton, positron, as well as antiproton fraction. Such universality may indicate they have a common origin. In this paper, we argue that these widespread excesses can be accounted for by a nearby supernova remnant surrounded by a giant molecular cloud. Secondary cosmic rays ($\rm p$, $\rm e^+$) are produced through the collisions between the primary cosmic ray nuclei from this supernova remnant and the molecular gas. Different from the background, which is produced by the ensemble of large amount of sources in the Milky Way, the local injected spectrum can be harder. The time-dependent transport of particles would make the propagated spectrum even harder. Under this scenario, the anomalies of both primary ($\rm p$, $\rm e^-$) and secondary ($\rm e^+$, $\rm \bar{p}/p$) cosmic rays can be properly interpreted. We further show that the TeV to sub-PeV anisotropy of proton is consistent with the observations if the local source is relatively young and lying at the anti-Galactic center direction.