Speaker
Description
Understanding the origin of the Ultra-High-Energy Cosmic Rays (UHECR) requires explaining features of their energy spectrum and arrival directions. Currently, modeling approaches neglect the time evolution of UHECR observables in the galactic magnetic field (GMF). This study focuses on the influence of the GMF on the arrival direction and spectrum of UHECR observed on Earth, emphasizing temporal and geometrical effects. Using CRPropa 3.2, we investigate the rigidity-dependent residence time of extragalactic cosmic rays entering our Galaxy. We probe both constant and time-varying extragalactic flux scenarios and find that UHECR entering the Milky Way can experience delays of hundreds of kiloyears relative to light. This temporal effect modifies the spectrum by introducing features such as an enhancement of the flux with a $R^{-1.2}$ dependence for rigidities $R \leq 10^{18}$ V, a suppression of particles between $10^{18}-10^{19}$ V, and a natural softening of spectra over time.
The comparatively short residence time of particles above a certain rigidity could naturally explain the narrow maximum rigidity distribution required to describe the UHECR spectrum and composition.