Origin of Galactic cosmic rays at sub-GeV energies

Determine the origin of Galactic cosmic rays, particularly those at sub-GeV energies, whose sources cannot currently be reliably traced because of observational limitations.

Background

The paper identifies the origin of Galactic cosmic rays as an unresolved astrophysical problem, with the greatest uncertainty affecting sub-GeV particles. Unlike higher-energy cosmic rays that can be indirectly traced through gamma-ray emission, sub-GeV cosmic rays are difficult to localize because the relevant gamma-ray observations have poor angular resolution and the MeV-band emission does not isolate the low-energy proton component responsible for ionization.

The study investigates ionized carbon ([C II]) as a possible spatially resolved tracer of the ionizing effects of low-energy cosmic rays in the supernova remnant RX J1713.7−3946. Although the observations and CLOUDY modelling constrain possible contributions from cosmic rays and ultraviolet radiation, they do not determine the Galactic cosmic-ray origin itself.

References

The origin of Galactic cosmic rays (CRs), particularly at sub-GeV energies, remains uncertain due to their difficulty in being traced.

— Observations of ionized carbon towards the $γ$-ray-bright supernova remnant RX J1713.7-3946  (2608.24181 - Thakur et al., 25 Aug 2026) in Abstract, p. 1; Section 1, Introduction