A Multi-messenger Search for a Nearby Microquasar Contributor to the Cosmic Ray Knee

TL;DR

This study explores whether known and potential microquasars can explain the cosmic-ray knee, finding that while known sources contribute little, an unidentified microquasar in the anti-Galactic center region could account for observed cosmic-ray features.

Contribution

It introduces the possibility that an undiscovered microquasar near Earth significantly influences the cosmic-ray knee region, based on gamma-ray and cosmic-ray data analysis.

Findings

Known microquasars contribute negligibly to the knee.

A hypothetical microquasar in the anti-Galactic center region can reproduce observed cosmic-ray spectra.

Unidentified microquasars may dominate the cosmic-ray knee features.

Abstract

Recently, LHAASO has detected five microquasars with high confidence, which are associated with SS 433, V4641 Sgr, GRS 1915+105, MAXI J1820+070, and Cygnus X-1, respectively. Except for Cygnus X-1, the maximum energies of gamma-ray photons emitted from these sources all exceed 100 TeV, strongly suggesting that microquasars are capable of accelerating cosmic-ray particles to energies above the PeV range. This work investigates the origin of the cosmic-ray knee region based on gamma-ray observational data from the aforementioned sources, combined with cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy observations. Calculations indicate that these known sources contribute negligibly to the cosmic-ray knee region. However, further joint analysis reveals that a single microquasar located in a region approximately on the 2.6 kiloparsec scale in the anti-Galactic center direction can reasonably reproduce the observed cosmic-ray proton, helium, and all-particle energy spectra, as well as anisotropy features detected near Earth. We propose that this region may host one or several unidentified microquasars or similar systems, whose accelerated cosmic rays could dominate the observational characteristics of the knee region.