Microquasar Remnants as Pevatrons Illuminating the Galactic Cosmic Ray Knee

TL;DR

This study models how microquasar remnants, influenced by the Galactic magnetic field, contribute to the cosmic ray knee, showing that nearby and recent remnants dominate the observed PeV bump.

Contribution

It introduces a simulation of anisotropic cosmic ray propagation from microquasars, highlighting the importance of magnetic connectivity and source history in explaining the CR knee.

Findings

Magnetic connectivity determines local flux enhancements.

The CR knee is mainly due to cumulative microquasar remnants.

A harder injection spectrum reproduces the PeV bump after propagation.

Abstract

Microquasars are primary candidates for Galactic PeVatrons, yet their collective contribution to the cosmic ray (CR) ``knee" remains poorly understood. We investigate this contribution by simulating anisotropic diffusive propagation through the Galactic magnetic field (GMF). Our results demonstrate that the GMF establishes a transport regime where magnetic connectivity between sources and the solar neighborhood determines the local flux. Active sources aligned with local GMF lines, such as Cygnus X-1, exhibit significant flux enhancements, while magnetically disconnected sources, such as V616 Mon, are strongly suppressed. By integrating source evolution with anisotropic transport, we show that the observed proton bump at the CR ``knee" is best reproduced by the cumulative contribution of microquasar remnants, which is often dominated by a few nearby or recent events, rather than the active ones alone. We find that a harder injection spectrum allows CRs from remnants to reproduce the PeV bump after propagation, as low-energy CRs have sufficient time to accumulate while high-energy CRs escape the Galactic plane. Our findings suggest that the integrated history of microquasar remnants, governed by the interplay of source age and magnetic connectivity, is the primary driver populating the observed CR ``knee''.