CRESCENDO: An on-the-fly Fokker-Planck Solver for Spectral Cosmic Rays in Cosmological Simulations

TL;DR

CRESCENDO is a novel on-the-fly Fokker-Planck solver that models the evolution of cosmic ray protons and electrons in cosmological simulations, enabling detailed study of non-thermal emissions and shock acceleration processes.

Contribution

It introduces an efficient, on-the-fly spectral CR evolution solver integrated into cosmological simulations, capturing acceleration, losses, and spectral changes of CR populations.

Findings

Successfully models CR injection and spectral evolution in galaxy clusters.

Reproduces radio relic morphology and spectral steepening.

Provides insights into non-thermal emissions in cluster mergers.

Abstract

Non-thermal emission from relativistic Cosmic Ray (CR) electrons gives insight into the strength and morphology of intra-cluster magnetic fields, as well as providing powerful tracers of structure formation shocks. Emission caused by CR protons on the other hand still challenges current observations and is therefore testing models of proton acceleration at intra-cluster shocks. Large-scale simulations including the effects of CRs have been difficult to achieve and have been mainly reduced to simulating an overall energy budget, or tracing CR populations in post-processing of simulation output and has often been done for either protons or electrons. We introduce CRESCENDO: Cosmic Ray Evolution with SpeCtral Electrons aND prOtons, an efficient on-the-fly Fokker-Planck solver to evolve distributions of CR protons and electrons within every resolution element of our simulation. The solver accounts for CR (re-)acceleration at intra-cluster shocks, based on results of recent PIC simulations, adiabatic changes and radiative losses of electrons. We show its performance in test cases as well as idealized galaxy cluster (GC) simulations. We apply the model to an idealized GC merger following best-fit parameters for CIZA J2242.4+5301-1 and study CR injection, radio relic morphology, spectral steepening and synchrotron emission.