Role of hadronic secondaries in the origin of radio halos

Determine the contribution of secondary electrons and positrons produced by hadronic proton–proton interactions to the emission and formation of cluster radio halos.

Background

Radio halos are commonly interpreted in terms of turbulent (re-)acceleration during cluster mergers, but hadronic models posit that secondary electrons from cosmic-ray proton collisions with the thermal intracluster medium contribute to, or even dominate, the halo electron population. Despite extensive radio and gamma-ray work—including the Abell 2256 analysis presented—quantifying the hadronic contribution remains unresolved. The authors note the pure hadronic scenario is disfavored by radio data for many systems and confront it here with Fermi-LAT constraints, but the general role of hadronic secondaries in radio halo origins is still unclear.