Origin of the relativistic electron pool and details of cosmic-ray transport/acceleration in clusters

Determine the origin of the non-thermal relativistic electron pool in galaxy clusters and establish the detailed cosmic-ray transport and acceleration mechanisms within intracluster media that produce the observed diffuse synchrotron emission.

Background

Diffuse synchrotron sources in merging galaxy clusters require a population of relativistic electrons and effective acceleration and transport mechanisms acting in the intracluster medium. While shocks and turbulence are implicated, the initial source of these electrons and the precise microphysics governing their transport and acceleration remain unsettled. The paper emphasizes that, despite new ultra-low-frequency LOFAR observations and gamma-ray constraints, these foundational issues persist as open questions of cluster non-thermal physics.