Microquasar remnants as hidden PeVatrons

TL;DR

This paper suggests that remnants of microquasars could be hidden sources of PeV cosmic rays, explaining some of the unidentified ultrahigh-energy gamma-ray sources observed by LHAASO.

Contribution

It introduces the idea that microquasar remnants can act as dark PeVatrons, producing high-energy gamma rays through cosmic ray interactions with molecular clouds.

Findings

Microquasar remnants can confine cosmic rays and produce gamma-ray emission.

Remnants of super-Eddington systems can accelerate particles up to 10 PeV.

This model explains several unidentified LHAASO gamma-ray sources.

Abstract

The Large High Altitude Air Shower Observatory (LHAASO) has revealed numerous ultrahigh-energy gamma-ray sources of unknown origin. We propose that a fraction of them can be explained by microquasar remnants, i.e., binary systems where mass transfer has ceased and the central engine is quenched. Cosmic rays injected during the active phase of a microquasar may remain confined within its cocoon and subsequently interact with nearby molecular clouds, producing bright gamma-ray emission through $pp$ collisions. Remnants of former super-Eddington systems can act as dark PeVatrons, releasing particles up to $\sim$10 PeV that illuminate surrounding clouds producing gamma rays reaching hundreds of TeV. This scenario provides a natural explanation for several unidentified Galactic LHAASO sources.