Cosmic rays, gamma rays and neutrinos from discrete black hole X-ray binary ejecta

TL;DR

This paper explores black hole X-ray binary ejecta as a potential source of high-energy cosmic rays, gamma rays, and neutrinos, suggesting they could contribute up to 5% of Galactic cosmic rays at PeV energies.

Contribution

It introduces a novel investigation of discrete black hole binary ejecta as cosmic ray sources, supported by multi-wavelength observations and modeling of particle acceleration and associated emissions.

Findings

Ejecta can accelerate particles up to ~2×10^{16} μ^{-1/2} eV.

Estimated contribution of ejecta to Galactic cosmic rays is about 1%, rising to 5% at PeV energies.

Predicted gamma-ray and neutrino spectra provide constraints for future detections.

Abstract

The origin of cosmic rays from outside the Solar system are unknown, as they are deflected by the interstellar magnetic field. Supernova remnants are the main candidate for cosmic rays up to PeV energies but due to lack of evidence, they cannot be concluded as the sources of the most energetic Galactic CRs. We investigate discrete ejecta produced in state transitions of black hole X-ray binary systems as a potential source of cosmic rays, motivated by recent $>100$ TeV $\gamma$-ray detections by LHAASO. Starting from MAXI J1820+070, we examine the multi-wavelength observations and find that efficient particle acceleration may take place (i.e. into a robust power-law), up to $\sim2\times 10^{16}\mu^{-1/2}$ eV, where $\mu$ is the ratio of particle energy to magnetic energy. From these calculations, we estimate the global contribution of ejecta to the entire Galactic spectrum to be $\sim1\%$, with the cosmic ray contribution rising to $\sim5\%$ at PeV energies, assuming roughly equal energy in non-thermal protons, non-thermal electrons and magnetic fields. In addition, we calculate associated $\gamma$-ray and neutrino spectra of the MAXI J1820+070 ejecta to investigate new detection methods with CTAO, which provide strong constraints on initial ejecta size of order $10^7$ Schwarzschild radii ($10^{-5}$ pc) assuming a period of adiabatic expansion.