Beyond the Local Void: A comprehensive view on the origins of the Amaterasu particle

Abstract: We use the reconstructed properties of the Amaterasu particle, the second-highest energy cosmic ray ever detected, to map out three-dimensional constraints on the location of its unknown source. We highlight possible astrophysical sources that are compatible with these regions and requirements. Among these, M82, a powerful starburst galaxy, stands out as a strong candidate due to its position and proximity. To derive our constraints, we use CRPropa 3 to model all relevant propagation effects, including deflections in the Galactic and extra-Galactic magnetic fields. We consider key input quantities such as source distance, position, energy, and the strength and coherence length of the extra-Galactic magnetic field as free parameters. We then infer constraints on these parameters by applying approximate Bayesian computation. We present our results, demonstrating the impact of different assumptions for the arrival mass of the Amaterasu particle and the systematic uncertainties on the energy scale.